Saab96

Hi

I want advice from you in Rennlist who has tons of knowledge about Porsche.
I have owned my Porsche for 7 years, The car runs well and has never had any problems, the car has full service history from new. I know from documentation that head studs were changed (to 993) when the car had been driven approx. 190000 kilometers, beyond this I have no information what has previously been done too the engine.
I have now performed (by myself) a "health check" of the engine.
My car is an 89 model 964 C4 driven approx. 270000 kilometers.The car uses approx. 0.5 liters of engine oil per 1000 kilometers.
My measurements and visual inspection have been performed on a cold engine, the car has not been driven in the last 2 months.
The visual inspection (of tightness between cylinder and head) shows that there is visible oil between the cylinders and heads on 3, 5 and 6. the rest is dry and I can not see that there have been any leaks on cylinders 1, 2 and 4 before. The engine is otherwise completely dry.

I have performed compression tests with the following result:
cylinder 1. 185 psi,
cylinder 2. 185 psi,
cylinder 3. 175 psi,
cylinder 4. 190 psi,
cylinder 5. 170 psi,
cylinder 6. 185 psi.

Cylinder leak test is performed with the following result:
cylinder 1. 13%,
cylinder 2. 17%,
cylinder 3. 13%,
cylinder 4.10%,
cylinder 5. 19%,
cylinder 6. 7%.

During the cylinder leak test, I heard leakage at the following locations, the sound is ranked from loudest to weakest:
Cylinder 1. crankcase, exhaust and intake,
cylinder 2. crankcase, exhaust and intake,
cylinder 3. crankcase, exhaust and intake,
cylinder 4. crankcase,
cylinder 5. crankcase , exhaust and intake,
cylinder 6. crankcase and intake.

The spark plugs were replaced for approx. 25000 kilometers ago and I have made a visual inspection of these, attached photos.

Cylinder 3-2-1

Cylinder 6-5-4



Based on the results of these tests, what do you recommend? Continue to be satisfied or total engine renovation, possibly head and new piston rings or new cylinder / pistons?

I thank you for all the answers and feedback.

F/51 LRS

If it were my car I'd plan on doing the top end; new rings, heads worked, reseal, etc.
Your compression looks pretty good, but the leak down numbers don't. If you're hearing leaking in your crankcase on every cylinder that leads me to believe you need new rings all around; the #3 & #6 spark plugs seem to support that since they look like they are coated with burnt oil and gunk. # 4&5 look quite good.

Being an '89, unless it's been updated you also have the early style heads that don't use a gasket. These tend to flex differently than the cylinder they're mated to and leak; probably what you're seeing. You can either have gasket channels machined into your cylinders/heads, or buy the updated 91+ cylinders, which are already machined and additionally have a slightly different profile for the head to sit more secure and not flex as much (I'd recommend this, though more expensive).

You can get down the rabbit hole VERY quickly depending on what you uncover tearing into things. I'm by far and away NOT the authority on these things, but the symptoms you talk about are very similar to the ones I had before my engine rebuild.

Hope that helps!

Saab96

Hi

And thanks for your answers, I have performed these tests on cold engine, would you recommend that I also perform these tests on a hot engine? Will it give me other numbers?

chsu74

My motor had cold leak down between 9-13% at 52K miles. Compression numbers matters little on a cold motor as long as they are consistent. Anything under 20% on a cold motor leak down is fine IMHO. Your 2 and 5 cylinder leak down numbers can be attributed to something as simple as tiny carbon build up. I would do a warm leak down before tearing into it if you are serious about a rebuild as your oil consumption is not that bad actually.

1 qt oil burn(not leak) every 600 miles and feel of down on power will be rebuild time for me. You are only half there on oil consumption. My motor burns a bit less than you but we are not that far apart.

F/51 LRS

Leak downs are supposed to be performed cold and compression tests are generally supposed to be performed warm (if you're trying to understand if you have good/high compression), if you do a compression test cold all you're looking for is consistency across all the cylinders to ensure there aren't any valvetrain issues unique to a cylinder.

At the end of the day your engine is fine, just probably a bit tired.

P356GT

Our engines can look like ”new” inside with 300,000 km and had a nice service according to the book :-)
How many km do you drive during the summer?
I have one 964 engine with same km as yours its been resealed during my stay home due to C19 but leaking from the left Cam chain housing but it will be dealt with this winter.
I have already bought new Cyl and pistons and more for a total renovation but the engine is really running good so I am waiting to renew it all.
Your oil consumption is also kind of fair from milage you mentioned.
Drive your 964 more and postpone the rebuild ;-)

Ha de fra Skåne

Saab96

Hi

Thank you for all the feedback, based on this I will postpone an engine renovation and look forward to a summer 2021 with a lot of porsche driving.
I unfortunately have more classic cars and the summer is short here I live, therefore the 964 is only driven approx. 1-2000 km every year.

Greetings from northern Norway.

Alan G.

Your oil use is within Porsche's guidelines, although the (US) standard of 1QT per 1000 miles always seemed high.
As others have said, the heads are past their prime, and the cylinder bases could use machine work, there are probably many more miles left in the engine if it has been cared for.
It will get slowly worse, but they usually keep on trucking,
Mine has 222,222 miles, the heads are toast, but everything else looked good when I split the case.
I wish I took my friend's advise to bolt on new heads and go, His 964 has 248,000 now., and mine would have more.