I got a coolant flush on my Carlo on 10/15 because I haven't had one in about two years and the car was running hot, today I found black gunk which looked to be oil in the reservoir shop is saying the upper and lower manifolds need to be replaced does that sound right? My Monte has 173k miles on it. Is there anything else I should check for also?

 

Yea the gaskets go bad. The entire manifolds do not need replaced, just the gaskets. Common issue with the 6th gens with the 3800.You can get upgraded metal gaskets from fel-pro if you still want to use dex. I did the metal gaskets and put the green stuff in.

 

You're right to question what the shop said and seek additional opinions and information. Are you sure the shop actually did a flush?

I almost never believe what repair shops say; been burned by them more times than I can remember which is why I do all my own work.

If the black gunk in your overflow reservoir looks kinda like misshapen globs like what you see in a lava lamp, it may be engine oil. Brown gelatinous gunk is caused by transmission fluid.

I'm compelled to declare that my expertise is with old iron, i.e., small-block Chevy (SBC) engines, but the basic principles and troubleshooting should apply.

Everything else being equal, it seems odd to me that engine oil would get into the cooling system. The cooling system is always under pressure unless there's a leak. The only way any kind of oil could make its way into the cooling system is if the oil's under more pressure than the cooling system, otherwise, coolant would leak out into the system where there is oil. You would more likely see evidence of coolant in your engine's crankcase than oil in your coolant. But, for the sake of argument, let's say the black gunk is engine oil. Studying the engine diagrams in your service manual will show you where all the water jackets in your engine block and cylinder head are in relation to the oil passages. The only way for oil to be "forced" into a water jacket would be if there's a crack in the block and/or the head. That sort of crack usually isn't that localized, it would propagate into the combustion chamber where coolant would be sucked in during the intake stroke then come out as steam in the exhaust, i.e., white smoke. Also, engine performance would be adversely affected. Another possibility may be a head gasket failure but that would be really noticeable by way of lots of white exhaust smoke and really bad engine performance.

Some questions for you:

• Are you experiencing any white exhaust smoke or drop in engine performance?
• Have you noticed changes in your coolant level?
• Have you noticed changes in your engine oil level?
• Have you noticed any (new) or larger fluid leaks where you normally park your car?

When you mentioned the shop said you need new upper and lower manifolds, I'm guessing you mean the intake and exhaust manifolds? The exhaust manifold is not included as part of the cooling system. On SBC engines, the role of the intake is only as a crossover for coolant from one cylinder bank to the other. On inline engines, the intake is not included as part of the cooling system. Their diagnosis makes no sense to me.

 

@wht02monte yeah I was putting in the orange stuff at first but I'll take a look at the the metal gaskets. Shop wants to charge 800. It's throwing me off because they didn't say anything about oil being in the reservoir for the first flush