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Coolant in engine oil


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I've been trying to find a straight forward answer to what exactly happens when coolant is in the engine oil.

 

So from the beginning, my step brother is a dork. He borrowed my dad's farm truck and while driving, a coolant hose failed. The engine was smoking and obviously overheating, however, he didn't know that you need to stop. Most likely, the heads are cracked because coolant now comes out of the tailpipe.

 

That was 2 years ago. The truck sat with some amount of coolant in the engine the whole time. So what damage did that cause? I've always heard it's bad, but why? Was it eating away at the metal?

 

When I first got into this truck, my plan was to just replace the engine with a used one, but I'm not finding one in my area do now I'm thinking I may just rebuild the top end. Can I simply pull the oil pan and inspect the crank?

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for a 1978?

 

at their healthiest, the blocks were very thin.

shameful time in history. I blew three chevies , rods out the front side of the blocks. unannounced and unexplained sometimes. All of them late 70s.

 

the good news..

there is a million more better gm v8s than that. :)

 

 

Go for a late 90s vortec swap, injection computer all of it. All iron 305 or 350. Easy to find, still supported today.

that empty engine bay is like a clean chalkboard.

 

a lot of potential.

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The motor has been swapped out once before. The engine that is in it is an '86. I thought about upgrading to fuel injection but that's a lot more than I want to get into right now. I really just want to get it drivable again with good power.

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The extent of damage depends on how long it ran that way. At best there is no damage, at worst some bearings got wiped out. These years are also notorious for the intake gaskets to let go because they were not very compatible with the Dexcool (red colored) coolant. I've got a 98 Yukon that had one of it's intake gaskets let loose, a bunch of the coolant went into the crank case on a -15 F day and it sat and idled like this for proably 10 minutes until I realized what had happened. Let's just say the dip stick was registering a nice milk shake in the crank case. I proceeded to drain it, replaced the intake gaskets, flushed the engine several times and it is now none the worse, runs as good as it ever did, oil pressure while driving still registers over 40 and it uses very little or no oil despite it's 215,000 rounds. Sounds like you're going to need to hunt down a cylinder head or two, replace the intake gaskets, new coolant (go with the green stuff) and flush the engine a few times and you'll probably be fine. A little coolant in the crankcase along with 5 quarts of oil at the time shouldn't have really hurt anything, the 350's are pretty tough.

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Thanks for the advice, ifixedit. I don't think this engine ran very long at all with coolant in the motor, aside from that day it overheated. My biggest concern was the length of time it sat with coolant in the crank case. I've heard before that it can corrode bearings, but I never understood why. I think I'll go ahead and rebuild the top end and hope for the best.

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A cheap way to check it out is fire it up put stop leak in it a run it. Put clean oil in it run it around a while, you could get miles out of it while your seeing what else is wrong with the truck.

 

 

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Did your brother drive the truck till it quit running? If so it could have started to seize up. If that is the case then the cylinder walls could be scored and the pistons wiped out. I would pull the heads and hope it just blew a gasket. That way you can check the heads and cylinder walls. If they look good then pull the pan and take a look at a couple of rod bearings and a couple of mains. If every thing looks good then all you are looking at is a gasket set to put it back together.

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Did your brother drive the truck till it quit running? If so it could have started to seize up. If that is the case then the cylinder walls could be scored and the pistons wiped out. I would pull the heads and hope it just blew a gasket. That way you can check the heads and cylinder walls. If they look good then pull the pan and take a look at a couple of rod bearings and a couple of mains. If every thing looks good then all you are looking at is a gasket set to put it back together.

 

Might not be bad advice just to be sure before you go to the trouble on the top end, especially if it ran a long time in the overheat condition. You've got to yank the heads anyways, wouldn't hurt to go a bit further. If you decide not to investigate the bearings and go ahead with just the top end, you will know what you have as soon as you start the engine and it warms up. You will either have pretty stable oil pressure of around 40 psi at start up and no lower than 20 - 25 psi at idle when the engine is warm, OR the oil pressure will be low when it starts and will drop like a rock as it warms up, it will also be smoking like a chimney, and likely a knock or two as well. If that's the case you know for sure you've got some wiped out rod and / or main bearings. Again the 350's are pretty tough and they will take some abuse, the main thing is there was oil in the pan at the time of the problem, even if there was coolant along with the oil, so I'd feel pretty confident there's no serious damage.

 

As far as the coolant sitting in the pan I don't think that would cause any major issues, it likely separated from the oil anyways and was the first thing to come out of the drain plug. As far as the stop leak goes, don't put that crap in your engine ever, especially if coolant is getting into the oil! You don't want that AND the coolant in the crank case circulating around, not a good combo and even more of a mess to flush!

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Thanks for the advice. I won't really know what I have until the top end is rebuilt. As it sits right now, I don't run the engine at all. When I first tried it when I got it home, it did start right up with ease, with a squirt of ether. But within seconds coolant was coming out of the exhaust and I turned the engine off. So idling to temp is out of the question. I do want to replace all the gaskets. Head, oil pan, valve covers, everything. In that process I'll put on new heads and inspect the rod bearings and cylinder walls. When I get to that point I'll post some pictures for a little feedback. I'm pretty handy around the garage, but by no means an expert. For the next couple weeks tho, I'm clearing out junk cars and semi-preparing for winter.

 

Keep the advice coming, it's always welcome. Thanks again for the replies I've already gotten.

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