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Discussion Starter #1
I have a 1986 300zx coupe, automatic with 92,000 miles. I have always changed the oil at 5k miles with synthentic and the car runs great. At about 85,000 miles, I've started using a quart of oil every 500 to 700miles. I can not see it coming out the exhaust, the underneath is bone dry, the plugs do not indicate any oil fouling, compression is great, and no oil leaks are evident on my garage floor. Could I have a problem with bad valve seals? I know many Japanese engines are prone to this due to the rubber compound reacting with high detergent oils cause them to become hard and brittle and lose sealing properties. Has anyone else experienced this on Zcars?
 

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Stop using synthetic oil

I used to run synthetic in Saab 99's and it was great! Then I tried it in an '89 Maxima and it was ****. If I were you, I'd switch to Castrol 20w-50 for one oil change. See if there is a difference.

Interestingly enough, I used my last 2 quarts of Mobile 1 to flush my wife's Volvo turbo. I'm tried and true Casrol, now.
 

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Synthetic is fine

It's not your oil. If fact conventional oil is more prone to problems than synthetic. The first thing you need to do is find out where the oil is going. If not out the exhast or a leak, then check under the hood to see if it is vaporizing. The best way to check this is to make a clean spot on top of your engine and drive around for about 100 miles. If this spot gets an abnormal amount of oily residue then look for leak somewhere. More than likely it will be a cracked hose.
 

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Discussion Starter #4
Re: Synthetic is fine

> It's not your oil. If fact conventional oil
> is more prone to problems than synthetic.
> The first thing you need to do is find out
> where the oil is going. If not out the
> exhast or a leak, then check under the hood
> to see if it is vaporizing. The best way to
> check this is to make a clean spot on top of
> your engine and drive around for about 100
> miles. If this spot gets an abnormal amount
> of oily residue then look for leak
> somewhere. More than likely it will be a
> cracked hose.
Ted - Thanks, I'm going try your suggestion. I've been using Castrol Syntec 10-50w in my other cars (86, Porsche 944 Turbo and an 84, 911 Carrera) for the past 5 years with no problems. I'm going to do a timing belt change within the next couple of weeks - I'll try to see if anything shows up during the change. Thanks again, John
 

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oil is oil

I used to work at a z-car shop in nashville, and with all the z-cars that we did oil changes on we used castrol 20-50.. alot of people questioned the 20-50, but there was never a car that came in there that was worked on by us that had knocking lifters, oil consumption, etc. all of the z-cars, especially the newer ones (84-96) run hot, and the 20-50 is the best... if theres still a question, use 10-40 in the winter months..
as far as the synthetic goes.. i don't think that theres enough evidence that the synthitic is that much better to justify the 3 dollar a quart price on it.. change it at least 3k and you'll never have a problem....
 

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Discussion Starter #6
Re: oil is oil

> I used to work at a z-car shop in nashville,
> and with all the z-cars that we did oil
> changes on we used castrol 20-50.. alot of
> people questioned the 20-50, but there was
> never a car that came in there that was
> worked on by us that had knocking lifters,
> oil consumption, etc. all of the z-cars,
> especially the newer ones (84-96) run hot,
> and the 20-50 is the best... if theres still
> a question, use 10-40 in the winter months..
> as far as the synthetic goes.. i don't think
> that theres enough evidence that the
> synthitic is that much better to justify the
> 3 dollar a quart price on it.. change it at
> least 3k and you'll never have a problem....
Skip,
Think you're right. The two reasons I've been using the synthectic is that I can get the Castrol Syntec wholesale by the case and I've heard that turbo's (also have a Porsche 944 turbo) love synthectic because synthectic oil doesn't coke in the turbo during cool down. The Porsche gets about the same mileage use as the Z so when it's oil change time, the Z gets half a case and the Porsche
gets the other half. The question is, I don't know if my oil loss problem is really directly related to the type of oil or not? Like you say - oil is oil. I was kind of leaning to the idea that maybe the valve stem seals were the culprit. I don't really know of any test to detect this other than to remove the rocker arms and have a look see. I do know thatone symton of bad valve stem seals was a puff of blue smoke on sudden acceleration or shifting but I don't see this happening either.
Thanks for the feedback.
JohnF
 
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