What Actually Happens When You Overheat an Engine

this BMW has a problem it

overheat

s So today we are going to drive it to the limit to see how long an

overheat

ed

engine

can last and then we are going to take the

engine

out, take it apart to see

what

really goes wrong

when

you cook. an engine, okay guys, come get sticks, who wants to go first? The short stick goes first, it's towards him, oh yeah, okay guys, we're all ready to burn this thing down, so let's do a lap a piece and let's Swap drivers as quickly as possible so we can keep heating up the engine and have a good chance of overheating it.

Now I don't get any pleasure from breaking something intentionally, but this old guy is already on his way out, so we thought we'd do it intentionally. Superheat it one last time so we can all see firsthand

what

happens

when

your engine overheats. Well, Adam, generally speaking, there are about five areas of concern when an engine overheats. The thermostat. A failure in the water pump. First on the list of things that could have failed will be our thermostat. Your cooling system is designed to keep the engine at an operating temperature that is neither too cold nor too hot, and this allows that temperature to remain in the middle.

The sweet spot, if you will, when the engine is cold, this thing is closed so no coolant flows into the radiator, it just stays in the engine and warms up until it reaches operating temperature and then as the coolant reaches the operating temperature. heats up the thermostat, the thermostat when heated expands and opens like a little valve and that allows coolant to flow into the radiator and disperse that heat into the atmosphere. Now if it is stuck it means no coolant is flowing. your radiator even when the temperature requires it, so if it's stuck closed it will overheat, warp things, blow a head gasket and if it's stuck open on the other side, it will run too cold, especially on a day like today where only there is about 45°F so these are critical it is a very simple, cheap and fairly easy part to replace wow wow wow the water pump is responsible for moving coolant through your cooling system pushing Passes through the radiator to dissipate heat.

This is a head gasket and is responsible for sealing the cylinder head to the engine head gasket block. 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 is because the heat

actually

warps the cylinder head or block, making the mating surfaces impossible to seal. In either case, a bad head gasket can mean loss of compression and leakage of oil to coolant or coolant to oil or both, or oil and/or coolant. in the combustion chambers, which are all bad, the car is running at about 18500 right now, which is a pretty normal operating temperature, but if we can get this to 240, 250, 260 and 300, then we're going to have problems and that's what we're looking for piston rings that are responsible for sealing the pistons to the cylinder walls and maintaining combustion compression in the combustion chamber.

These can wear out due to poor engine oil lubrication and this can happen due to low oil level or infrequent oil changes. or oil temperatures that get too high so the oil can no longer do its job and once the piston rings wear out you no longer have compression and your engine won't be happy at idle, this thing won't overheat , so it's time to take some drastic measures and speed up this puppy, they say it can take up to 4 years to be a chef, but with today's sponsor chef, Unity, I can do it in minutes. Being a chef is about strength, precision and intuition.

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The instructions are here on the food. Go to cook donuts at unity.com or click the link in the description and use my code donut 50 to get 50% off your first order of Cook Unity meals. Try them for yourself D America America God all beautiful sky from the sea to Shining no goodbye my sweet prince well it's been a tough couple of days sacrificing our Darling but we did it all in the name of science and now it's time for science begins, so we have to take the engine out of the car and take it apart to find out what really happened to it after yesterday's abuse.

Take the engine out of the car and now it's time to find out if we really caused any damage to it, so we'll find out while we take it apart. I think the first thing we should do is a leak 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 leakage there is, so basically the idea here is that we have compressed air at about 100 PSI coming into the tool and then we have this regulator where we can dial things in so basically we want to get dialed up to this zero point here at the beginning of the meter now Jerry has the hose installed on cylinder number one plug it in there and then blow air into the cylinder and tell us how bad it is the leak, it's pretty bad, you can hear a leak now, the other thing you should mention is that we're at top dead center, uh, on the combustion stroke on cylinder number one, so all the valves are closed.

It's meant to be a sealed cylinder, but in our case it's not, we have a high leak of about 75%, which is pretty bad, we can also run some smoke in there, that's true, and see if it comes out. some smoke to give us a visual, then that's true because it's one thing to know that you have a leak, it's one thing to know that you have a cylinder that has an incorrect leak value, but it's another thing to know where that leak is coming from to be able to fix it. So once you do this, you can listen and try to hear where the air is coming from.

In our case, it's pretty obvious it's coming from the intake port or intake valves and you have to keep in mind that an engine is just a giant air pump. and that air must remain in the cylinders to be pumped and converted into power and if that is not the case, that means it is coming from somewhere. Cylinder one is leaking, let's move on to cylinder 2 and see how bad that cylinder is. Oh, this one is real. Bad, yes it sounds like that so you can tell the size of the leak by the noise it makes, it's like a hiss or yes this is a Huer it only has a 45% leak but as you'll notice you know the green area and green always means good. having some leaks is normal YY waa we have a thick leak 80% we have about 55% leaks there 55 okay it's in green we're at about 22 and 1 12% leaks cylinders 5 are still alive hell yeah it's okay , so the leak test did not return good results, which is not too surprising, honestly the most surprising thing about this is that cylinders 5 and 6 came back technically fine, a leak of 22 1 12%, not great, but it's a lot better than the 75 45 85. and 55% leak down 85 yeah that's a lot we might find something there yeah that's probably our problem cylinder uh to see when we move on mhm now that was interesting because Most of the leak sounded like it was coming through the valves, so I'm expecting to see some type of valve 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 right, we get out our thermostat, this is a 68°C mishimoto, it looks good.

It's not that old, we put it here. The only damage caused is this small piece of rubber that used to help seal the actual opening surface on the thermostat. It looks like it's been cooked a bit and just delaminated, which it will. a little worse for sealing the cooling system halves, really no big deal now let's see what's going on with our water pump. We replaced this water pump on this engine with a nice one with metal vanes. From the factory, on some cars, you will have a plastic impeller, which are the blades that push the fluid through the system and over time, especially with overheating, and you know that if you spend any time at the rev limit, that It can take its toll. plastic blades and this thing has survived well, it's taken a lot of abuse but it's in good shape so this is not the problem so the water pump is crossed off the list and we'll keep moving down okay, I'm removing the head bolts now so we can take the head off and that will allow us to see what's going on with the head gasket and if there's any damage to the individual cylinders, whether it's the cylinder walls, the pistons, the piston rings. piston, valves, let's see everything.

Once we open this up and I suspect if we're going to find any damage, that's where everything will be fine, let's see what's going on inside, this looks pretty good, no marks, no evidence of oil in the coolant or coolant in the cylinders or something the top of the pistons look pretty good, they aren't, yeah everything is pretty clean so far. I'm impressed with what I say, we have to go deeper, we have to enter the belly of the Beast, well, let's launch. the head up there look at it look at the head gasket look at the valves Okay, like when you're an old man and they look at your coronary arteries and they're all clogged up from all that sugar and carbohydrates, yeah, you like cholesterol. all that cholesterol plaque build up this is what it looks like just blocking these passages these coolant passages uh this is crazy okay although this factory head gasket looks mostly good like all the parts which are supposed to be sealed independently of each other.

They were sealed independently of each other, except there is one problem and it's our coolant lines. There should be little holes on the side of each of the cylinders that are responsible for allowing the coolant to come up through the head and remove the heat from the head and you know, bring it on. all to the radiator and you can see several of these and we have drilled a few since we removed it but a lot of them are completely clogged or at least partially clogged now it's supposed to be a small hole but uh the holes have been pretty well blocked in across the board so that doesn't help, that means we're not getting good coolant flow through the head and the heat is just building up there and that takes a toll on the engine as a whole. that's the closest thing we have to a smoking gun so far.

Alright, the next thing we're going to do is scrape all the old gasket material and all the dirt off the mating surface of the head and then we're done. I can use a ruler and some feeler gauges and check to see if the head is warped at this point. I don't really think it's marginally, but I don't think it's too crazy and that's mostly based on how well the head gasket looked like it had been on the roof, so when you look at a head and want to check to see if it's warped or not, you should know that each cylinder head will have an allowable warp tolerance because First of all, it is almost impossible to have something perfectly flat, so everything will have a little warp and there will be a tolerance to tell you how much is acceptable and anything beyond After that, you will have to send it to the machine shop so they can have it.

They skim it back flat and the tolerance on this engine is extremely bright and doughy, so the tolerance on this m52 is a staggering 2000 inches, which is incredibly small, it's a low tolerance and it's very flat, but the tools to do this check this tolerance is pretty simple you have a machinist's ruler so our ruler is precision ground and you put that ruler in different ways and you measure the blades across the head and if you can slide the blade right feeler gauge, it means you have a gap right now, this is 2000 of an inch, that is, 051 mm and I will see if I can get it.

Look, okay, that goes in there very easily and I can move it around a little bit, so I know that that space is more than 2000 of an inch, it's probably worth mentioning that four, five and even 6000 are sometimes acceptable tolerances, it just depends of the engine, so it's not too surprising to see us go to 6000 of an inch, which is three times the acceptable limit, uh, come on, boy, oh.boy, look at that right there, okay, let's go to 7000, let's go hit the big point, no and now we're getting big, let's put it, let's go right here, okay, but look, that's why you put this at an angle .

Because when I did it in this it was accomplished, but when I got here it did well because the head can deform in many different ways, it can bow, it can twist, you know? Buckle up, yes, and it's a good idea to keep it. Continue until you can no longer run the feeler gauge to find out what your most warped section is because there will usually also be a specification for how much material you can remove from the head to skim it without having to use it. a thicker head gasket or you know, potentially it's time to buy a new head, we have some warping, which we do if you were to draw a line, it would be like this, it would be like a half pipe, yeah, and now.

This is not the only contact surface that must be flat, the block that joins the side of the head must also be flat, so if you have come this far you must also clean the block and measure its deformation and, uh, also You can We've skimmed it well so we know we have some leaky valves, but we want to see how leaky the valves are, so Joby has created a small block of wood with a hole in it and that will cover these. ports here now while the valves are closed in this position obviously you can see the springs are holding them down these essentially should be closed now they're going to leak a little bit just because everything is leaking a little bit nothing is completely sealed , so what?

What we're going to do is fill this with some fluid, 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 off the valve seats, there are a couple of leaking exhaust valves on cylinder one, so let's see how bubbly the intake bubbles are. In a perfect world, what you would want to see is zero bubbles because that pressure is pretty low compared to what the spring does. It's going to be low during the combustion cycle oh Jerry, can I drain it for you, no, no, okay, the first set of valves is leaking, now let's find out if the rest are.

I bet they're Jimmy. 20 dollars for that. that's it 20 bucks yeah that's pretty bad both Val looks like it's leaking and excessive amounts of leaking the best that's pretty good okay so out of 12 sets of valves we have one set that barely has leaks and 11 that do. There really is leakage, so I think this is a big part of the loss and power we were feeling over the last few days at the track. It can be fixed, but I want to see what's going on with the bottom now since our head was so deformed. You might expect the block to be equally warped but generally speaking when you have an aluminum head and an iron block they won't warp at the same time if that makes sense and that's because they are different materials so they expand and contract at different rates with different temperatures and since they are bolted together like an aluminum head as it gets very hot and expands more than the block it tries to come out and it will warp even though it is bolted to a block that is not deformed. so let's turn it over and take out the rest of the stuff.

It's time to disassemble the rotating assembly. You're going to push the piston down. Yes, here we are. This is the piston skirt and that will interact with the cylinder wall. As it goes up and down it does this motion so you can get a lot of wear down there and you can see it's clean so the first one looks pretty good but let's take the rest out and look at all of them and then we'll evaluate it well so as we take it apart the rotating assembly, we looked at a lot of greased engine components, like the bearings and the rings and things like that, so you might be wondering since we've been talking about overheating. engine is more of a cooling system issue, which is true, but if you significantly overheat your car's cooling system, the oil temperature will also increase and when the oil temperature gets too high, say like 275° at 300° a, it's not like that.

It's no longer doing its job as a lubricator and you're going to get really accelerated wear on things like the bearings, the rings, the cam lobes, all the parts of the engine that the oil is responsible for protecting, and with that we have all of our pistons. and if we do a quick little inspection of our rod bearings, they all look pretty good, the valine oil did its job, no marks on the bearing, now it looks like probably the worst one is piston 3, cylinder 3, we are suffering some wear through coating. on the bearing, but other than that, I mean, these things are great.

The piston skirts look good. The rings look good. The tops of the pistons look good, yes, and everything has been relatively clean too. There is no mud buildup or anything like that. It's the engine. much better than I expected, we warmed it up but didn't heat it up enough for the oil to fail, but still let's take the crank off and look at the crank bearings, look at that to see if maybe there is a problem. there we fixed that, we have all the main crank caps loose and ready to remove, let's see what the bearings look like and see if there is any damage to the main crank journals based on what the crank bearings look like.

I think let's go. To be good, we have some wear, but nothing crazy, no indentations, no digging. I mean it looks pretty normal for a motor with that many miles on it and I think these are all going to look pretty similar so let's just pull them out and take a look, I mean if the top looks good the bottom probably looks pretty good, yes they look very similar to the other sides, a little wear but nothing crazy, yes they look pretty healthy, okay we should look at the boot, yes we could. Well, this is a pretty beefy crank, it's heavy, I think everything here is pretty good, and to that end, let's talk about the problems we

actually

had.

We had leaky valves, leaky valves on the intake and exhaust side, so that's bad for generating power. and it will help you overheat what else we had some warping in the head and block where that surface meets a lot more on the head the aluminum head was out of spec pretty bad and the head gasket was also clogged in the oil passages coolant, so that contributes to burning the valves and knowing the leaky valves sooner and overheating the whole engine, so I think if we remove the head, remove the block and make the valve seats red, we could go back to put this together, we definitely could.

A great engine took a beating and could continue eating. You know it won't be the case for all engines, but this engine is pretty impressive. Now Joby put this back together and then I don't know what we should do to put it back together. this car or I think we probably have a better engine I have a better idea I have a better idea it's also a six cylinder yeah okay guys this has been an interesting video to make me feel bad at first but Now I feel a lot. It's better to know how well this engine survived and we can save it.

We can rebuild this engine. Put it in another car. We have the technology. Thank you all very much for watching this. Everything else at Donut, goodbye.