What Actually Happens When You Overheat an Engine

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 at him 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 to 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 this puppy out they say it can take up to 4 years to be a chef but with today's sponsor cook Unity I can do it in minutes being a chef is all about strength precision and intuition impeccable cook Unity is the first ever Chef to you meal delivery service every meal is carefully crafted using fresh seasonal produce highlighting Whole Foods and supporting 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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 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 skimmed the head skimm the block and had the valve seats red done we could put this thing back together we definitely could 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 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

Channel: Donut

Views: 1,852,712

Keywords: donut, donut media, cars, up to speed, moneypit, jeremiah burton, zach jobe

Id: 7749aWcQZ2Y

Length: 21min 44sec (1304 seconds)

Published: Fri Jan 26 2024