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Thread: Oil test shows coolant contamination in 4.9!

  1. #1
    caddydaddy's Avatar
    caddydaddy is offline Cadillac Owners Connoisseur
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    Exclamation Oil test shows coolant contamination in 4.9!

    I had the oil in my '94 Deville tested by Blackstone Labs, and they said the following:

    "The oil sample from your Cadillac tested positive for coolant contamination. Potassium, silicon, and sodium are the hallmarks of the anti-freeze. We had expected to find wear higher but that wasn't the case. Universal averages for the 4.9L are based on an oil run of ~3,200 miles. If you keep your oil runs around the 4,000 mile mark you should be able to live with this problem for a while. If you have noticed any loss of anti-freeze then you can be sure a problem exists. Insolubles were low, showing good oil filtration. Check back to keep an eye on your engine."

    Since intake manifold gasket leaks are common on these engines, is that the first place I should look? I have noticed a slight coolant loss, but other than that, nothing unusual. No overheating or rough running. The engine has 140,100 miles and it was 4,069 miles before the oil was changed with Rotella 15w-40.


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  3. #2
    noahsdad's Avatar
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    Re: Oil test shows coolant contamination in 4.9!

    Intake gaskets rarely result in coolant contaminating the oil. Hate to be the bearer of bad news, but you might be looking at head gaskets here. Get a cylinder pressure test done to diagnose.

    Do you keep up with the cooling system maintenance and use the sealant pellets? They won't help if the gasket is already gone, but Blackstone's assessment indicates the contamination isn't significant enough to cause damage yet, so it may just be a weak spot that the sealer could shore up.

  4. #3
    caddydaddy's Avatar
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    Re: Oil test shows coolant contamination in 4.9!

    Yes, I do keep up with cooling system maintenance. And the previous owner did to, I could tell he used the supplements tablets. It had 94k when I bought it, and I've changed the coolant twice in the 50k miles I've owned it, and used the supplement tablets.
    Is it possible for it to leak between the timing chain cover and get in that way? When I first bought the car, there was a coolant leak in that area, and it was some loose bolts. I'm not sure if a bad gasket there could cause coolant to leak into the engine.
    Yeah, I'd really hate it to be a head gasket, it's a very nice Deville for it's age, and runs great! I'm really bummed out about this!

  5. #4
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    Re: Oil test shows coolant contamination in 4.9!

    OK, an update: I tested the cooling system for hydrocarbons using a block tester http://www.rxauto.com/blocktest.htm . I did this test three times, and the fluid did not change color. So either the head gasket leak is really small, or the leak is not from the heads. My only other guess would be a leaking intake manifold gasket, where it is leaking into the lifter valley and down into the engine oil.

    Any thoughts?

  6. #5
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    Re: Oil test shows coolant contamination in 4.9!

    It could be oil cooler connections inside of the radiator. Head gaskets on 4.9s are good. Do not worry much, just drive it and check the coolant level frequently.

  7. #6
    caddydaddy's Avatar
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    Re: Oil test shows coolant contamination in 4.9!

    It has a new radiator, so it's something in the engine. I'm not too worried about it now, but leaks don't get better or lessen as time goes by! I'd really like to keep this car another 2 or 3 years, so I'd like to find out exactly what's going on with it now.


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