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1991 Cadillac Sedan deVille
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530 Posts
Discussion Starter #1
I have a '91 Sedan deVille with the 4.9L. The car has 59k actual miles, oil changed EVERY 3K miles. Inside the engine looks like new.

I have put about 700 miles on the car since I got it (and I changed the oil) and about 300 miles into it, I had to add 1/2 quart of oil. I checked it again today, about 400 miles later and it is 1/2 quart low again. There are NO leaks and I do not see any smoke from the car, nor do I smell oil burning and there is none in the coolant.

The car has new EGR valve and fuel injectors (though I know replacing those should have nothing to do with it).

I am running "Super Tech" 10w30 oil in it, with an ACDelco oil filter. Should I be using different oil? This oil has the "star burst" on it, so I assumed it was an ok oil to use.

I asked my mechanic about this and he said it may be where the car has set for awhile... he said just drive it and see if it gets better. I don't know.

Thanks.
 

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2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
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26,323 Posts
FWIW, you're throwing money away changing the oil that often, and it's of zero benefit to any part of the engine. You should do some reading in the Cadillac Technical Archives (in the black tab at the top of the page), on the OLM.

The oil you're using is fine. If you want, you could switch to a fleet oil, with a higher zinc content. It would be beneficial to an engine with flat tappet lifters.

Is the car always driven sedately? Carbon buildup in the ring grooves can cause excessive consumption.

Is the PCV valve gummed up?
 

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1991 Cadillac Sedan deVille
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530 Posts
Discussion Starter #3
Thanks.

Well I didn't change the oil that often, but the previous owner did. She (94 year old lady) bought the car new and she wrote down every oil change and it was changed every 3000 miles. Also, I am sure the car was driven very leisurely and I have followed suit, trying not to damage the car. Perhaps I should start driving more aggressively?

I have no idea about the PCV valve.

Thanks.

FWIW, you're throwing money away changing the oil that often, and it's of zero benefit to any part of the engine. You should do some reading in the Cadillac Technical Archives (in the black tab at the top of the page), on the OLM.

The oil you're using is fine. If you want, you could switch to a fleet oil, with a higher zinc content. It would be beneficial to an engine with flat tappet lifters.

Is the car always driven sedately? Carbon buildup in the ring grooves can cause excessive consumption.

Is the PCV valve gummed up?
 

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1991 Cadillac Brougham D'Elegance 5.7 Litre, 1994 DeVille
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6,796 Posts
When my 4.9 started loosing oil it was the PCV valve. It checked out OK but for the few bucks they cost I changed it anyway and problem gone.
 

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1991 Cadillac Sedan deVille
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530 Posts
Discussion Starter #7
Thanks, I will go ahead and change it. I know on some cars it is super easy to change, not sure about this one though. I will look for it tomorrow/get out the service manual.
 

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1991 Cadillac Brougham D'Elegance 5.7 Litre, 1994 DeVille
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Thanks, I will go ahead and change it. I know on some cars it is super easy to change, not sure about this one though. I will look for it tomorrow/get out the service manual.
It's right at the top of the front valve cover and just pulls out. On a 91 you might have to remove the upper plastic cover to get to it if it's still on there.
 

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1991 Cadillac Sedan deVille
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530 Posts
Discussion Starter #10
When my 4.9 started loosing oil it was the PCV valve. It checked out OK but for the few bucks they cost I changed it anyway and problem gone.
It's right at the top of the front valve cover and just pulls out. On a 91 you might have to remove the upper plastic cover to get to it if it's still on there.
Yep, it was right there. I wasn't sure when I looked, so I got out my service manual and it said it was right where you said and yeah I did have to remove that plastic panel. The new one wasn't much, so I went ahead and got one, though I am not sure if the old one was bad or not. It still rattled, which the manual said if it didn't rattle it was bad, which I already knew. It read "AC Rochester" on it, so I am assuming it was the original and probably needed to be changed anyway since the car just turned 60k.

I refilled it with oil, it was 1/2 quart low. I will check it again next weekend and see if it is still full, or if it is low again. Hopefully that was the losing oil issue.

I also got the thermostat replaced today... also the original.

Thanks again.
 
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