[Sohail1]

Hello every one. I have been reading the forum for a lil while after i purchased my first F355 1995 with 26000 miles. This is my first post and im looking an answer from some on experience with 355's. I did a PPI in houston before the purchase and it all came out clean. When the car got here i kew it needed a 30k service done which i got done. My question to you guys is that before the service the dealership did a leak down test cold and came back to me saying 4 of my cylinders were leaking less then 8% and the rest 4 were leaking 23% to 30%. I have heard that the leak down test is supposed to be done at operating temperature and not cold. Will it make a difference in my leak down numbers or am in getting ready for a valve guide replacment. Thanks for any kind of advice i can get from you all


Sohail

 

[4kids3fish]

If the test is meant to be done at operating temps then doing it cold would not give reliable numbers IMO. You are measuring pressure leakage through small gaps, & those gaps will change (and the results change) with increased/decreased temperature.

I admit to being ignorant about the exact nature of a leak-down test, but assume it measures cylinder compression loss over a standard period of time. I would have thought this would be mainly a factor of bore/piston wear, ring condition & valve/seat sealing and not the valve guides, unless badly worn guides then mean that the valves seat incorrectly??
:nuts:

Anyone have any more experience with this?

Valve guide wear is often indicated by blowing smoke after extended idling or going down a long hill. The increased manifold vacuum pulls more top-end oil down the valve-stem / valve-guide gap and it then drops a nice cloud of smoke when you hit the throttle again.

 

[Andrew]

Sohail,

Welcome to the site, I hope you enjoy your new F355 and that we can help in your ownership experience.

About your question, the results should improve at operating temperatures. The pistons are likely to expand more than the block making them tighter. Same for the rubber seals.

 

[Boxer]

Hello every one. I have been reading the forum for a lil while after i purchased my first F355 1995 with 26000 miles. This is my first post and im looking an answer from some on experience with 355's. I did a PPI in houston before the purchase and it all came out clean. When the car got here i kew it needed a 30k service done which i got done. My question to you guys is that before the service the dealership did a leak down test cold and came back to me saying 4 of my cylinders were leaking less then 8% and the rest 4 were leaking 23% to 30%. I have heard that the leak down test is supposed to be done at operating temperature and not cold. Will it make a difference in my leak down numbers or am in getting ready for a valve guide replacment. Thanks for any kind of advice i can get from you all


Sohail

Sohail,

I doubt it is a value guide issue (the F355 Buyers Guide in the members section has some information on the Valve Guide issues). It sound like more of a valve seat problem or piston/ring wear.

Good luck.

 

[blackonblack360f1]

Sohail,


About your question, the results should improve at operating temperatures. The pistons are likely to expand more than the block making them tighter. Same for the rubber seals.

i agree, i also think it would be rare to see piston/ring wear that early in a cars life. its still a baby