Compresion #s What should I do?

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Mar 28, 2006
Basalt, Co
From front to back
90, 60, 65, 80, 55, 90

I am trying to decide if I want to convert to a 2fe or go with a V8. I already have a complete 3fe for the parts, but my 2f is gettin up there in miles. 216k. It still gets 16+ mpg, but the motor is leaking from everywhere and seems like it could snowball into a huge project. I just want to be able to drive it for a while if I make the effort. It is desmogged, so a cleaner running engine is one of the goals too.

What is, and how do I do, a leak down test? What does it tell me beyond the compression #s?

I would say that those are some bad numbers. I don't think a leak down test is going to tell you anything you don't already know. Time to rebuild or replace.
My bet is that its a valve issue. Pull the head and get it rebuilt (valve job/ resurface). While its apart if there is little to no ridge you could do a re-ring of the pistons. At 216 k it is getting kinda old, only another 100k left. All that being said I would get a Vortec and do the swap.

Dynosoar :zilla:
16mpg and comp numbers that bad don't add up to me. I'd check the valve clearance and test it again. Did you have the throttle wide open when doing the comp test?
608, 604, 603, 606, 605, 604

Put in a diesel!:beer:
Adjust the valves & do a leak-down. It'll tell you whether it's rings or valves (& which valves at that).

Your mpg suggests nothing really evil unless you drive 30mph for long stretches at a time (& at Basalt's altitude which I'd guess is 9-10,000', no?).

A leak-down tests each cylinder at a regulated pressure (I use 100 psi for convenience) & records the "residual" as an effiency percent. It requires a compressor, regulator, & pressure gauge. It's best done on a warm engine, with each cylinder succesively at TDC. If a cylinder is below 95% & you can hear air moving through the oil filler, the problem is rings. Through the carb it's an intake valve. Through the exhaust, you guessed it.
Last edited:
Thanks Tinker.
I will investigate further to what I can come up with
Was the compression guage a new one? It might be off some but the difference between cylinders is showing a problem.

What altitude are you at? At 5000ft on a new engine the compression will be around 120 psi. The engine looks like it has some issues. I would adjust the valves and do a wet /dry compression test to learn more. Also try some seafoam or the water down the carb to see if you have a lot of carbon buildup. Search for the threads talking about it.
Last edited:
those are some really low numbers. but 16 mpg is something to envy, are you sure your compression gage is in good shape? myself have recently replaced my head- can't figure it out as my gage gets readings about 20 to 25 psi less with a new head, did scrape the carbon off the top of the pistons while i was in there, but still i questoin the gage as none of this adds up, yes , valves are adjusted and been rechecked.
Yeah my gage is pretty beat up, but I did the low numbers a couple times just to check, and they came out the same.

My only travel is on a highway with a cruising speed of 60-65, speed limit is 55 in most spots, but I just go with traffic. I don't try to beat anyone of the line, or anywhere really. My mpg is pretty consistant at around 16. I know its pretty good for a cruiser, that is why I am hesitant to scrap the motor just cause it leaks so much. It feels pretty stong aswell.

I am going to try the leak down test this weekend. It seems like the way to get a good idea of where the motor is at.

Users who are viewing this thread

Top Bottom