A friend of mine, Steve from Manchester has been looking to purchase a 300ZX and from what I have read on the site in the past, when he asked my advice, I told him to have a compression test done before parting with his money.

Anyway he has been to the garage today and he watched them as they did a dry test on the front 4 cylinders that were easy to get to, all figures were almost identical at just over 130. He phoned me up and I did a quick search on the forum which suggested the figures were a bit low. So I told him he needed a wet test (with oil). They did this and the figures were unchanged.

This is totally beyong my knowledge, I assumed that if oil was added the figure would go up? Also on just speaking to him I gather the throttle bodies were not held open. Would that make any difference?

Apparently the engine runs really well and is at 63,000km

Any advise will be gratefully received so I can let him know if you guys think it is a problem of not.

I'd say try another compression tester. Very odd that they are all down. Usually just a few.

 

Also. PLEAAAAAAAASSSSSSSSSEEEEEEE resize your signature.

....oil is added to get a better seal. It could be a case of coked up valves.....which is why the test may not change with the oil...?

You MUST get a reading on the back two also.

They are the cylinders most likely to have problems (Im not saying there are any)

Wide open throttle and do them all at the same time.

I would be looking for 150 ish at least.

No increase on a wet test might indicate valve seat wear as the culpret.

Like Pete said, you need all 6 tested or its a waste of time, personally I would rather do the test myself or take a competent friend to do it for me, not saying they would be hiding anything but unfortuately these days people do. If they are all low then either its fooked or they are doing something wrong during the test.

Steve was helping him do the test by turning the engine over, the garage apparently said it was a new gauge, so I assume should be OK. Just phoned him again for more details. Just turned the engine over 3 times or so and did not press the throttle at all, both I understand are wrong.

He is planning to go back again tomorrow evening, the garage are then doing all 6, something to do with it taking too long to to the back two today (apparenly they are harder to get to?)

So he needs to turn the engine over longer and press the throttle?

 

any more ideas on why the dry and wet would be the same? Could it be that the low reading is false because the test is not done correctly and the engine is in such good condition that the wet test is the same?

All 6 plugs have to be out. Engine warm.

 

Turn over 6 or 8 times till the needle wont go any higher, and must have throtle to the floor.

 

I did mine on the front 4 only and had 130.(left the back to plugs in)

Did it properly then had 150 except the no.6 (back right) which had 90 and was f***ed. Did wet on no.6 and it was 150, so the rings where fooked.

 

Getting to the back ones doesnt take long at all, just gotta take the balance bar off and a couple of pipes.

was the engine up to temperature??

Engine was apparently showing up to temp. They left it running for 20 minutes before test.

 

Any more ideas on why the dry and wet would be the same?

thats very strange as that usually indicates a valve problem.but to have valves gone on all 4 front cylinders is unlightly.and it would run ruffer than a badgers arse.and probaly smoke.or it can indicate the cylinder gasket is leaking but then again for them to have failed on all of the front 4 cylinders is also very remote.how much oil did they add?

thats very strange as that usually indicates a valve problem.but to have valves gone on all 4 front cylinders is unlightly.and it would run ruffer than a badgers arse.and probaly smoke.or it can indicate the cylinder gasket is leaking but then again for them to have failed on all of the front 4 cylinders is also very remote.how much oil did they add?

Not sure how much oil I will ask Steve if he knows

You'll have to wait till its tested properly. Like I said, my results where totally different!

yip as mentioned you HAVE to do it with wide open throttle. thats the most common reason for all cyls to be low. or a choked air filter!