Hi, I'm thinking about purchasing a 1991 Z28. I went to check it out at the dealership yesterday, it ran and drove smoothly without idle problems, and the electronics all seemed fine, but it has a little problem under the hood. There is oil in the coolant reservoir! The car only has 90K miles on it, and everything else seems fine, plus I could negotiate the price to around $2500. It seems like a bad head or head gasket, I just need to know:

1) Is it more likely a problem with the head gasket, or the heads themselves (Since it doesn't have extremely high mileage)

2)I'm pretty repair savvy, and would be fine doing the fix myself, but can I change the heads/gaskets without removing the entire engine from the car? (I've had people tell me that I need to , and others tell me I don't. I need a definite answer.)

 

More importantly is their coolant in the oil? If their is a way for the oil to travel out their is probably a way for coolant to travel in. And if the car has been run with coolant/oil mixed you can kill internal engine bearings pretty quick. Look for milkshake looking oil, though being a dealership they might have changed the oil recently.

Gaskets are easier to break than cracking/warping a head, but you wouldn't know without tearing it down. The heads can be removed without pulling the engine, and that is the very least you will be doing in this case.

I would stay away unless you are ok with an entire engine rebuild...




Unless it is trans fluid mixed with the coolant which can happen with a busted radiator, as their is a trans cooler built in. If so thats not a big deal, new radiator, done.

 

Ditto to whats been said above, but about taking the engine out: you shouldnt need to, what i did was take the hood and fenders off and just sat on the wheels. It made things MUCH easier, no straining my back bending over to work on it, everything was right in front of me, and i was more comfortable sitting lol.

A word to the wise however, if you do this be careful, your neighborhoods HOA may not take a likeing to it. Cover the car up real well when your not working on it and park the car so the front isnt visible (or at least harder to see) from the road. I did it in my driveway and the hoa got on my @ss real quick about it.

But being you dont know how long the car was ran like that, your taking a pretty good risk of having other problems down the road such as bearings go bad if you didnt do an entire rebuild.

Also something to consider, if it was something fairly small and simple to fix, the dealer probably would have fixed it to sell with a higher price tag, no?

 

Another angle is that this is a 91 Z28. A 92 would be more compelling, but they are visually identical aside form the the 25th anniversary stuff in 92. But the 91-92 Z28s are some of the more rare incarnations of thirdgen performance models. TTA's and 1LE type cars are more rare, but they only made less than 20,000 Z28's in 91 (12,000) and 92(5,000) combined. Consider they made around 300,000 camaros in 68 and 69, and they made 100,000 z28's in 1984 alone.

So if the car is being sold as low mile car, then I would assume it's in decent physical shape. Straight body, decent paint, nice interior, etc. If that's the case and it's a nice looking car, given the relative rarity of those 91-92 Z28's, it might be worth the $2500 even if the motor has serious or even terminal issues. Rebuilding a stock L98 isnt that hard or expensive as long as you keep it stock. You could do it between $500 and $1500 if you do a lot of the stuff yourself. Just dotn thow some garbage goodwrench 350 in it.

Now you may not be wanting to jump into grease monkey mode on a car you just bought, you may just be wanting a daily driver or just a nice looking thirdgen with less maintenance/work involved... in that case, just go on to the next car. Coolant and oil mixing is a very bad sign and it's very possible it's a terminal problem. The block could be cracked from not running enough antifreeze in the winter, there's really no telling until you tear it apart and find out.

So even at $2000+ the car could be a really decent deal just because of the rarity of what it is, and it may be worth fixing. But that really depends on the person because in this case "Fixing" may mean starting over with a whole new block and building a new engine for it. Not everyone is willing or able to do all that. But if you ever wanted to learn how to do an LS1 swap... this is a good car to do it.

If the car looks like garbage and is beat up, then it's not worth bothering with.

 

I have been repairing cars professionally for about 38 years and I have never seen a case where a cracked block or head gasket caused oil intrusion into the coolant. I can't say that it is impossible, it would just have to be extremely rare as I've worked on maybe 1000 small block Chevy V8s and have worked with other professionals who worked on 1000s more. I have of course seen many cases of the reverse. The reason for this is that the coolant is under pressure throughout the system, where as oil is only pressurized in the galleries. There are no pressurized oil passages to the cylinder heads, or passing through the head gasket, so the possibility that a head gasket failure could cause oil to enter the cooling system is almost nil.

There is however an engine oil cooler attached to the block at the filter adapter. I have seen a few cases, on various makes(VW, Toyota) that use the same oil/coolant heat exchanger, where the vanes leak pressurized oil into the coolant at the cooler. The nature of the break can prevent coolant from passing back into the oil. Also, as post #2 mentions, the trans cooler in the radiator is also a likely suspect. One quick way to check for actual oil intrusion is to look at the condition of the hoses. Oil will turn heater or radiator hoses into mush pretty quickly. The hoses will become very soft and swell up significantly. This is easy to spot with just a squeeze of the hose.

 

I had oil in my coolant when I had a cylinder bore crack. Not a lot, but you could smell motor oil (and gasoline) in the coolant and it had a strange look to it. Weird things can happen, just wanted the guy to be aware that it's not a safe assumption that it's as "minor" as even a head gasket. He will have to dig into it and see.

 

Good call. Like I said, it isn't impossible.