What Actually Happens When You Overheat an Engine
Summary
TLDRThe 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
🚗 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.
🛠️ 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.
❄️ 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.
📏 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.
👍 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.
Mindmap
Keywords
💡overheating
💡head gasket
💡water pump
💡thermostat
💡cylinder head
💡valves
💡piston rings
💡bearings
💡coolant passages
💡leakdown test
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
do you like coffee do you like donuts do
you like us well guess what February
18th you're going to have the rare
opportunity to experience all those
things at the exact same time if you can
handle it announcing the first ever
donut media Cruis in at the Peterson
Automotive Museum in Los Angeles we're
going to have all of the dut cars all of
the hosts an exclusive merch collab that
you'll be the first to have access to
and a bunch more stuff if you want to
come you can just show up or hit the
link below RSVP required for a cart dude
really looking forward to meeting you
guys rubbing some elbows going to be
some cool vendors there Honda's coming
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
bye
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