Hello.

I will very shortly own a 2005 g35 sedan MT RWD.
- what was the compression when new ? (220)
- at what point would you consider addressing a low compression (rings, valves, head gasket etc). How low would you wait ? (subjective answer expected).
- does the engine have to be rotated for this test?
- ballpark expected cost to check - $200?

Yes, I did a search before posting this. Unfruitfull.

thank you.

 

First off, the compression test needs to be done on cold motor. Secondly, the compression test may or may not reveal an oil consumption issue with your Revup motor. Yes, the motor does have to be rotated to test the compression. They'll do the test cylinder by cylinder.

The issue with the Revup's is weak rings and that's what would get replaced if you were going to rebuild a Revup with OC problems, however, most just do an OEM short block swap which is hit or miss. If I had a Revup with OC that wasn't under warranty, I'd rebuild it myself with stronger rings. Nissan purposely used loose rings to reduce frictional losses. In the Revup, the practice backfired and they made the rings too weak.

 

The factory service manual shows the following for compression:
Standard: 184 psi / 300 RPM
Minimum: 142 psi / 300 RPM
Differential limit between cylinders: 15 psi / 300 RPM

I would want to address it soon if it was serious.

The engine does not have to be rotated manually, but it does need to be turned over via the starter.

$200 seems kinda high...I'd expect closer to $100.

 

thanks Dave. Much appreciate the note. If you -or anyone else out there- knows the compression when new on this engine, please let me know. I suspect 220-230 psi, and that anything under 190 psi means power is going to be down noticeably. kind regards

 

The FSM says to warm up the engine before performing the test. Why are you recommending it be done cold?

 

Better to do on a warm motor. A cold motor will not give accurate numbers. (More comp than there is @ operating temp.)

 

I understand that the thermal expansion of the metal will increase the compression numbers, but therein lies the problem. The motor will loose heat as you conduct the test leading to differences in compression numbers as you work across the cylinders. A compression test on a VQ could take a while. By having a cold motor, you take out the thermal bias. I'm focused more on big swings in pressure between cylinders. If 5 cylinders show 160-180 psi and 1 cylinder shows 145psi, you know that cylinder likely has a problem. I then warm the motor a test the cylinder again. If it improves and gets within spec, then I usually won't worry about it. If it doesn't, there's a problem. Just my opinion.