98 S70 T5 A Couple Of Engine Diagnostic Questions

[msm15]

I went to look at a 1998 s70 t5 today, the engine bay was in pretty poor shape, the engine turned over - although not very smoothly but wouldnt start at all, so here is my question: Knowing nothing at all about the history of the car - what can a compression test tell you ?

My assumptions are as follows:

1:If the engine ran out of oil for some reason - whatever it might be - the engine would lock up and wouldnt turn over.
A compression test with good results would take that possibility out - not to mention the fact that the engine turned over

2: If the timing belt broke while the engine was going some valves would hit each other and bend and cause lack of compression by not sealing.
A compression test with good results would also rule that out

3: If the timing belt was replaced but not aligned properly the valves would still hit each other and would also cause no compression by not sealing
A compression test with good results should also rule this out

If someone could enlighten me on these topics and the truth of these statements it would be greatly appreciated.


When I spoke to the seller (a wholesale car dealer who knows nothing about the cars history) he said the mechanic said maybe the timing belt broke, or it wasnt aligned properly, when I popped the hood there was oil all over and the PCV hoses were broken connected in the wrong places etc. etc. but the timing belt was on and looked in very good shape - couldnt tell if it was new

I didnt do a compression test, fuel pressure test, or spark test yet I may go back and check the car out, but I was wondering if my assumptions listed above were correct.

Oh yeah there were no codes - battery was disconnected so I guess the system didnt store any, if there ever were


thanks all

[Ozark Lee]

You are pretty much right on. If scenario number 1 is the case the compression test won't tell you anything since the motor won't turn over at all. I wouldn't eliminate the possibility that it will turn over but the rod bearings or main bearings are destroyed, you won't know that until you actually get it to run.

If the timing belt broke while running but it has since been replaced then there will definitely be cylinders with low / no compression.

If the belt is only off by 1 tooth you will still get compression but it will run like crap. More than 1 tooth puts you in the danger zone of valve damage that will show up as low compression, even if the car never ran that way.

Your torx bits, a fuel pressure gauge, a compression gauge, and a spark plug wrench will tell you where the problem lies.

...Lee

[msm15]

thanks Lee, if I do a compression test I will post back with the findings