What Actually Happens When You Overheat an Engine

Summary

The hosts intentionally overheat a BMW engine to test its limits. They perform tests showing most cylinders have bad compression leakage. Removing the head reveals clogged coolant passageways likely causing overheating. Valve seats are extremely worn causing loss of power. Surprisingly, apart from warped heads and bad valves, the bottom end looks healthy. The oil protected well against overheating damage. With new head work and valves, the solid engine could be rebuilt.

Takeaways

• 😊The video involves intentionally overheating a BMW engine to test how long it can last before failure.
• 🔥They run laps in the car, revving the engine to increase heat until it overheats.
• 🛠After overheating the engine, they tear it down to diagnose issues and find the root causes.
• ❗Major issues found: warped cylinder head, leaky valves, clogged coolant passages.
• 👍Despite abuse, bottom end and internals are in decent shape, oil system protected well.
• 🔧They methodically check components: thermostat, water pump, head gasket, head, block.
• 😀Final verdict is the engine survived remarkably well, but does need some repairs.
• 🔨Head needs skimming, valves need attention, then it could run again.
• 🏁Key overheating failures: thermostat, water pump, head gasket, cylinder head, piston rings.
• 💡Takeaway: modern engines can survive some abuse if oil system protects well.

Q & A

What is the main goal of this experiment?

The main goal is to intentionally overheat the engine of an old BMW to its limit, in order to observe what fails inside the engine when it overheats.

What are some of the key components that can fail when an engine overheats?

Some key components that can fail include the thermostat, water pump, head gasket, cylinder head, and piston rings.

What does a leakdown test help determine?

A leakdown test helps determine the condition of the cylinders and how much compression is being lost due to leaks.

What was the result of the leakdown test on this BMW engine?

The leakdown test showed very high leakage percentages, especially on cylinders 1, 2, 3 and 4, indicating significant loss of compression.

What was causing the coolant passageways to get blocked in the cylinder head?

The coolant passageways were getting blocked due to buildup of deposits and sediments over time, restricting coolant flow.

How much warpage was found in the cylinder head?

The cylinder head was warped by 0.007 inches, which is way beyond the allowable tolerance of 0.002 inches for this BMW engine.

What was the main issue found with the valves?

11 out of the 12 sets of valves were found to be excessively leaky, resulting in loss of compression.

What protected the bottom end components from damage?

The high quality full synthetic oil protected the bearings, piston rings and other bottom end components from heat damage.

Could this engine be rebuilt and reused?

Yes, with some repairs like skimming the head, valve work and gasket replacement, this engine could be rebuilt and reused.

What could be done to prevent such overheating failures?

Regular maintenance like coolant flushes, valve adjustments, high quality oil and keeping temps in check could prevent such overheating issues.

Outlines

00:00

🚗 Discussing how to intentionally overheat a BMW engine

The paragraph introduces the plan to intentionally overheat a BMW engine that already has overheating issues, by driving it hard in laps to push it to its limits. It mentions the goal is to see how long an overheated engine can last before failure, then tear it down to examine what fails inside. The driver order is decided by drawing sticks.

05:00

🛠️ Tearing down and examining the damaged BMW engine

This paragraph describes removing and disassembling the BMW engine after the overheating experiment to inspect internal damage. Several diagnostic tests are conducted, finding worn thermostat rubber, leaky cylinders, and clogged coolant passages. The head is checked and found to be warped. The bottom end looks surprisingly good, with some wear but no failures from overheated oil.

10:01

❄️ Discussing how the cooling system works

This paragraph provides background details on how an engine cooling system functions. It covers components like the thermostat, water pump, head gasket and explains their purpose in regulating operating temperature. It highlights five key areas impacted by overheating.

15:03

📏 Checking for cylinder head warpage

This paragraph examines whether the BMW cylinder head is warped from overheating. A straight edge and feeler gauges are used to check for gaps exceeding the allowable tolerance. Warpage over 0.007 inches is found, indicating the head needs to be machined for flatness.

20:03

👍 Determining the engine is rebuildable despite damage

The closing paragraph concludes although there is damage like warped heads and leaky valves, the bottom end survived well. So the engine could be rebuilt with some new parts and installed into another car, having held up better than expected.

Keywords

💡overheating

Overheating is one of the main themes and problems explored in the video. It refers to when an engine gets too hot, usually from lack of sufficient cooling. Overheating can damage many engine components like the head gasket, piston rings, bearings, etc. The hosts intentionally overheat the BMW engine in the video to test and demonstrate the effects.

💡head gasket

The head gasket seals the cylinder head to the engine block. It can fail due to overheating, allowing coolant and oil to mix or leak into the combustion chambers. The hosts remove the head in the video and find that the head gasket survived well despite the overheating.

💡water pump

The water pump circulates coolant through the engine to dissipate heat. Failure of the water pump could contribute to overheating. The hosts find that the upgraded metal water pump survived the abuse well.

💡thermostat

The thermostat controls coolant flow to regulate operating temperature. If stuck shut, it could cause overheating. The hosts find only minor damage to the thermostat after overheating the engine.

💡cylinder head

The cylinder head houses the valves and forms part of the combustion chamber. It is susceptible to warping from extreme heat, preventing proper sealing. The hosts find significant warpage in the aluminum BMW head after overheating.

💡valves

The intake and exhaust valves control flow in and out of the combustion chambers. Leaking valves reduce compression and power. The hosts find nearly all the valves are leaking significantly after overheating the engine.

💡piston rings

The piston rings seal the combustion chamber and pistons against cylinder walls. Overheating can lead to ring failure. Despite abuse, the hosts find the BMW's piston rings survived remarkably well.

💡bearings

Bearings allow smooth rotation of engine components like the crankshaft. Overheating can affect oil lubrication and damage bearings. The video shows only minor bearing wear despite intentional overheating.

💡coolant passages

Coolant passages in the head and gasket allow circulation to cool the head. The hosts find these passages clogged, contributing to overheating failure.

💡leakdown test

This test indicates bad sealing by measuring air leakage from cylinders. The hosts perform it and find extreme leakage, confirming serious damage from overheating.

Highlights

We're going to intentionally overheat this BMW engine to see what fails.

Typically when overheating an engine, there are 5 main areas of concern: the thermostat, water pump, head gasket, cylinder head, and piston rings.

The thermostat regulates engine temperature by controlling coolant flow. If stuck shut, the engine can overheat.

The water pump circulates coolant to dissipate heat. Failure can cause overheating.

Head gaskets seal the cylinder head and block. Overheating can warp surfaces, causing leaks.

We're going to take this BMW engine apart after overheating it to see what damage occurred.

The leak down test showed significant loss of compression, indicating internal leaks.

We found the head gasket was still sealing, but coolant passages were clogged, restricting flow.

The cylinder head was warped beyond the allowable tolerance, contributing to overheating.

11 out of 12 valve sets were leaking significantly, lowering power and worsening overheating.

Despite overheating, the bottom end looked surprisingly healthy - oil had protected it.

Main issues were leaky valves, a warped head, clogged coolant passages in the head gasket.

With some repairs this engine could be rebuilt and reused instead of replaced.

The engine survived remarkably well considering the overheating abuse it endured.

We can save and rebuild this BMW engine by fixing the valves, resurfacing the head, and replacing head gasket.

Transcripts

this BMW has a problem it overheats So

today we're going to be driving it to

the limit to see how long an overheated

engine can last and then we're going to

pull the engine take it apart to see

what really fails when you cook an

engine all right boys come draw sticks

who wants to go

first short stick goes

first it's

atam oh yeah all right boys we are all

ready to burn this thing so we're going

to do one lap a piece and we're going to

swap drivers as quickly as possible so

we can keep heating the engine and give

ourselves a good chance of overheating

the thing now it brings me no pleasure

to intentionally break something but

this old boy is already on his way out

so we thought we'd intentionally

overheat it one last time so that we can

all see firsthand what happens when your

engine overheats all right

Adam typically speaking there are about

five areas of concern when overheating

an engine the thermostat a water pump

failure head gasket failure a warped

cylinder head and your piston rings

first on the list of things that could

have failed is going to be our

thermostat your cooling system is meant

to keep your engine at operating

temperature not too cold and not too hot

and this allows that temperature to be

kind of kept in the middle in The Sweet

Spot if you will now when the engine is

cold this thing is closed so that no

coolant is Flowing out to your radiator

it's just staying in your engine and

warming up getting up to operating

temperature and then as that coolant

gets up to operating temperature it

warms up the thermostat the thermostat

when it gets warm expands and opens like

like a little valve and that allows

coolant to flow out to your radiator and

disperse that heat into the atmosphere

now if this is stuck shut that means

that no coolant is flowing through your

radiator even when the temperature would

necessitate that so if this is stuck

shut you're going to overheat you're

going to warp stuff you're going to blow

a head gasket and if it's stuck open on

the other side of that you'll run too

cold especially on a day like today

where it's only about 45° F so these are

critical it's a very simple cheap part

and pretty easy to replace

go go go go

[Music]

go the water pump is responsible for

moving coolant through your cooling

system pushing it through the radiator

to dissipate

[Music]

Heat this is a head gasket and it's

responsible for sealing the head to the

block of your engine head gaskets can

fail due to overheating too much

cylinder pressure and of course

degradation of the gasket itself often

when a head gasket fails due to

overheating it's because the heat

actually warps the head and or the block

making the mating surfaces impossible to

seal in any case a failed head gasket

can mean loss of compression and leaking

oil into coolant or coolant into oil or

both or oil and or coolant into the

combustion Chambers which are all bad

[Music]

the car is running at about 18500 right

now which is a pretty normal operating

temperature but if we can get this thing

up to the 240s 250s 260s 300 then we're

going to have problems and that's what

we're looking

for piston rings are responsible for

sealing the Pistons to the cylinder

walls and keeping combustion compression

in the combustion chamber these can wear

out due to poor lubrication from the

engine oil and this can happen due to

low oil level too infrequent of oil

changes or oil temps that go far too

high so the oil can't do its job anymore

and once your piston rings wear out you

no longer have compression and your

engine won't be happy dead

center this thing won't overheat so time

to take some drastic measures and rev

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[Music]

[Music]

yourself

D

America

America

God all

beautiful sky from sea to

Shining

[Music]

[Music]

no goodbye my sweet

prince

[Music]

well it's been a difficult couple days

euthanizing our baby boy but we did it

all in the name of Science and now it's

time for the science to begin so we need

to pull the engine from the car and take

it apart to find out what actually

happened to it after yesterday's

[Music]

abuse all right we got the engine out of

the car and now it's time to find out if

we really did any damage to it so we'll

find out as we take it apart I think the

first thing we should do though is a

leak down test let's do it we'll put

compressed air from our air compressor

into the cylinder and then essentially

look at the gauge to see how much leak

down there is so basically the idea here

is that we've got shop Air at about 100

PSI coming into the tool and then we've

got this regulator that we can dial

things in so basically we want to get

dialed to this zero point here uh at the

beginning of the gauge now Jerry's got

the hose installed on cylinder number

one plug her in there and then it'll run

air into the cylinder and tell us how

badly it's leaking

is pretty bad you can hear a leak now

the other thing to mention is that we're

at top dead center uh on the combustion

stroke in cylinder number one so all the

valves are closed it's meant to be a

sealed up cylinder but in our case it's

not we've got a high about 75% leak

which is pretty bad we can also run some

smoke in there that's true and see if uh

any smoke comes out to give us a visual

so that's true because it's one thing to

know that you have a leak it's one thing

to know you've got a cylinder that has a

bad leak down value but it's another

thing to know where that leak's coming

from so that you can fix it so once you

do this you can either listen to try to

hear where the air is coming from in our

case it's pretty obvious it's coming

from the intake port or the intake

valves and you got to keep in mind an

engine is just a giant air pump and that

that air needs to stay in the cylinders

to be pumped to turn into Power and if

that's not the case that means it's

coming out somewhere cylinder one got a

leak let's move on to cylinder 2 see how

bad that cylinder is oh this one's real

bad yeah it sounds like it so you can

tell the size of the leak by the noise

that it makes it's like whistling

or yeah this is a Huer it's only leaking

45% but as you may notice you know the

green area and green always means good

having some leakage is normal YY waa we

got a fat leak

80% we're about 55% leakage there 55 all

right it's in the green we're at about

22 and 1 12% leakage cylinder 5es still

alive heck yeah all right so the leak

down test did not return good results

which is not too surprising honestly the

most surprising thing about this is that

cylinder 5 and six did come back

technically okay a 22 1 12% leak down

it's not great but it's much better than

the 75 45 85 and 55% leak down 85 yeah

that's a lot we might find something in

there yeah that's probably our problem

cylinder uh to look at when we pull

ahead mhm now it was interesting because

most of the leakage sounded like it was

coming through the valves so I'm

expecting to see some sort of valve

damage or seat damage so let's see if we

can find all the things that are wrong

let's take it apart let's do

it all right we got our thermostat out

this is a mishimoto 68° C it looks okay

it's not that old we put it in here the

only Damage Done is this little piece of

rubber that used to help seal the actual

surface that opens on the thermostat it

looks like it's been cooked a little bit

and just kind of delaminated which will

make it a little bit worse at sealing

the sort of the halves of the cool Co in

system it's really not that big of a

deal now let's see what's going on with

our water

pump we've replaced this water pump on

this engine with a nice metal bladed one

from the factory on some cars you'll

have a plastic impeller which is the

blades that drive the fluid through the

system and over time especially with

overheating and you know if you spend

any time at the rev limit that can take

a a real toll on the plastic blades and

uh this thing has survived well it's had

a lot of abuse but it's in fine shape so

this ain't the problem so water pump is

checked off the list and uh we'll keep

moving

[Music]

downwards all right I'm removing the

headbolts now so we can take the head

off and that will let us see what's

going on with the head gasket and if

there's any damage in the individual

cylinders to either the cylinder walls

the Pistons the piston rings the valves

we're going to see everything once we

get this thing open and I suspect if

we're going to find any damage that

that's where it'll be all right let's

see what's going on

inside this looks pretty good no scoring

no evidence of like oil in the coolant

or coolant in the cylinders or anything

like that the tops of the Pistons look

pretty good they're not yeah

everything's pretty clean so far I'm

impressed with what I'm saying we have

to go deeper we must into the belly of

the Beast well let's throw the head up

there look at it look at the head gasket

look at the valves Okay so like when

you're a old man and they look at your

coronary arteries and they're all

clogged up from all that sugar and carbs

you yeah like cholesterol all that

cholesterol build up the plaque this is

what it looks like just blocking these

passageways these coolant uh passageways

this is

insane okay so while this Factory head

gasket does look mostly okay like all of

the parts that are supposed to be sealed

independently of one another were sealed

independently of one another except

there's one problem and it's our coolant

passageways there should be little

little pin holes next to each of the

cylinders that are responsible for

letting coolant travel up through the

head and remove heat from the head and

you know bring it all to the radiator

and uh you can see several of these and

we've poked a few of them through since

taking it off but a lot of these are

fully clogged or at least partially

clogged now it's just supposed to be a

small hole but uh the holes have been

pretty well blocked uh across the board

so that doesn't help that means that

we're not getting good coolant flow

through the head and heat is just

building up there and uh that takes a

toll on the engine as a whole that is

the closest thing we've got to a Smoking

Gun so far all right the next thing

we're going to do is scrape all the old

gasket material and all the gunk off the

mating surface of the head and then

we'll be able to use a straight edge and

some feelers gauges and check to see if

the head is Warped at this point I don't

really think it's going to be maybe

marginally but I don't think it'll be

too crazy and that's mostly based on

just how well it looked like the head

gasket had been ceiling so when you're

looking at a head and you want to check

to see whether or not it's warped you

got to know that every head will will

have a tolerance for allowable warpage

because first off it's near impossible

to have anything perfectly flat so

everything's going to have a little bit

of a warp to it and there will be a

tolerance to tell you how much is

acceptable and anything beyond that you

need to send to the Machine Shop to have

them skim it to get it back to flat and

the Tolerance on this engine is

extremely bright and

pasty so the Tolerance on this m52 is an

astounding 2000 of an inch that's

incredibly small that's a low tolerance

and it's very flat but the tools to do

this to check this tolerance is pretty

simple you've got a machinist straight

edge so our straight edge is precision

ground and you put that straight edge a

few different ways and feelers gauge

across the head and if you can slip the

feeler gauge through well it means

you've got a gap right now this is 2000

of an inch that's

051 mm and see if I can get oh look okay

that goes in there super easy and I can

wiggle it a little bit so I already know

that that Gap is more than 2,000 of an

in it's probably worth mentioning that

four five even 6,000 are sometimes

acceptable tolerances just depends on

the engine so it's not really too

surprising to see that let's just go to

6,000 of an inch that's three times the

acceptable limit uh let's

go boy oh boy look at that right through

there it's all right let's go to 7,000

let's go hit the big spot no and now

we're getting we're getting big let's

put it let's go straight

here

okay but see that's why you put this on

an angle cuz when I did it on this it

got through but when I went here it did

it right because the head can warp in a

lot of different ways it can bow it can

twist it can you know Buckle yeah and it

is a good idea to keep going until you

can't get the feeler gauge through

anymore so that you know what your most

warped section is because there will

also usually be a spec for how much

material you can remove from the head in

order to skim it without either having

to use a thicker head gasket or you know

potentially just being like time to get

a new head we got some warpage the thing

we do if you were to draw a line it

would but it would be like this it would

be like a half pipe yeah and now this

isn't the only mating surface that needs

to be flat the block that meets up with

the side of the head also needs to be

flat so if you've gone this far you also

need to clean up the block and measure

it for warpness and uh you can also have

it

[Music]

skimmed

all right so we know we got some leaky

valves but we want to see how leaky of

valves are they so Joby has fashioned up

a little block of wood uh a hole in it

with a hole in it and that's going to

cover these ports right here now while

the valves are closed in this position

obviously you can see the Springs are

keeping them pushed down these

essentially should be closed now they're

going to leak a little bit just uh cuz

everything's a little leaky nothing's

completely sealed so what we're going to

do is we're going to uh fill this with a

little bit of fluid job's going to put a

block plate on it and then we're going

to put some compressed air in there and

see if we get any bubbles coming up from

the valve

seats those are a couple of leaky

exhaust valves on cylinder one so let's

see how bubbly the intake

are bubbly in a perfect world what you

would want to see is zero bubbles

because that pressure is pretty low

compared to what the spring is going to

be under during the combustion cycle oh

Jerry I can drain it for you don't don't

okay the first set of valves are leaky

now let's find out if the rest of them

are I bet they are Jimmy 20 bucks on it

that's it 20 bucks deal yeah that's

pretty bad a both

Val wa looks like it's leaking wa

excessive amounts of leakage leak about

the best that's pretty good

wa all right so out of 12 sets of valves

we have one set that's hardly leaking

and 11 that are really leaking so I

think this is a big part of the uh loss

and power that we were feeling over the

last few track days it is fixable but uh

I want to see what's going on with the

bottom end now since our head was so

warped you might expect the block to be

equally warped but generally speaking

when you've got an aluminum head and an

iron block they won't warp at the same

time if that makes sense and that's

because they're different materials so

they expand and contract at different

rates with different temperatures and

since they're bolted to each other like

an aluminum head as it gets super hot

and expands more than the block does

it tries to get out and will warp even

though it's bolted to a block that isn't

warped so let's flip it over and take

the rest of the stuff out of

it time to take the rotating assembly

apart you're going to push the Piston

down yeah here we are this is the skirt

of the piston and that will interact

with the cylinder wall as it goes up and

down kind of doing this move uh so you

can get a lot of wear there and you can

see it's clean all right so the first

one looks pretty good but let's take the

rest out look at them all and then we'll

assess all right so as we're taking

apart the rotating assembly we're

looking at a bunch of oiled components

of the engine like the bearings and the

rings and things like that so you might

be wondering since we've been talking

about overheating the engine that's more

of a cooling system thing right which

yeah is true but if you overheat the

cooling system in your car significantly

your oil temps will also rise and when

your oil temps get too high say like

275° fenhe 300° fenhe it doesn't do its

job as a lubricator as well anymore and

you'll get really accelerated wear on

things like the bearings the Rings the

cam lobes all the engine parts that oil

is responsible for protecting

all right and with that we have all of

our Pistons out and if we do a quick

little inspection of our rod bearings

they all look pretty good that valine

oil did its job there's no scoring on

the bearing now we look probably the

worst one is piston 3 cylinder 3 we're

getting some wear through the coating on

the bearing but other than that I mean

uh these things are great skirts of the

Pistons look good the Rings look good

tops of the Pistons look good yeah and

everything's been relatively clean too

there's no like sludge buildup or

anything like that it's engine it's a

lot better than I was expecting we got

it hot but we didn't get it hot enough

to have the oil fail but we're still

going to pull out the crank and see uh

the crank bearings look at that see if

maybe there's an issue

there fix that all right we've got all

the crank main Caps loose and ready to

pull them off see how the bearings look

and see if there's any damage on the

main journals of the crank based on how

the rod bearings looked I think we going

to be okay okay we got some wear but

nothing crazy no gouges no digging I

mean that looks pretty normal for for an

engine with this many miles on it and I

think all of these are going to look

fairly similar so let's just pull them

all and take a

[Music]

gander I mean if the tops look good

probably the bottoms look pretty

good yep these look very similar to the

other sides a little bit of wear but

nothing crazy yeah those look pretty

healthy all right should we look at the

cranking yeah we might as well this is a

pretty beefy crank it is it's heavy I

think everything here is is pretty good

and so to that end let's let's talk

about what issues we really had we had

leaky valves leaky valves on intake and

exhaust side so that's bad for making

power and will help you overheat what

else we had some warpage of the head and

the block where that surface meets much

more on the head the aluminum head was

out of spec pretty bad and that head

gasket was also clogged up in the

coolant passages so that will contribute

to burning your valves and and and

getting you know leaky valves sooner and

overheating your whole engine so I think

if we skimm the head skimm the block and

had the valve seats Reed done we could

put this thing back together we

definitely could do you like sick cars

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out now if you'll excuse me it's way

past my

bedtime this is a great engine took a

beating and could keep on eating this is

you know not going to be the case for

every engine but this engine pretty

impressive now Joby put this thing back

together and then I don't know what

should we do put it back in this car or

I think we probably have better engine I

got a better idea we got a better idea

it's also a six-cylinder yeah all right

guys this has been an interesting video

to make uh it felt bad at the beginning

but now I feel a lot better knowing how

well this engine survived and we can

save this we can rebuild this engine put

it in another car we have the technology

thank you guys so much for watching this

everything else at donut bye

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