Compression testing (Eunos Roadster 1.8)

[drophead]

Here's the background info: Last summer one of the heater hoses (at the back of the engine bay) decided to enter the next life and perished in the middle of rush traffic. Cue lots of swearing and a temp needle zinging to 'H' on the gauge quicker than a quick thing. I managed, after a minute or so, to get myself in a safe position to stop. All of my coolant had pd out in that time too.

Roll on to now when I've finally had the chance to start working on it, I've replaced both heater hoses, the CAS O ring seal and the Rocker cover seal too just to make doubly sure that no hot oil is going to be ruining any pipes soon!

After talking to some of the old boys who live down my street, who are currently working on this little beauty...







...they told me that I've most likely warped and cracked the head due to the intense heat. So I bung out the old compression tester to see the tell tale signs of a cracked head. However, the results have turned out like this:



I've ignored the first test as I think I didn't screw the compression tester on correctly.

What do people think of those results? I was told anything below 90psi meant that I had cracked the head but to my eyes, it seems the engine may have just survived it. Opinions are very welcome as I am about as beginner as you can get with mechanics. My cobwebbed filled wallet has brought about this sudden desire to DIY with regards to the engine!

[HeatonNorris]

I'm no expert, but I had a similar failure on my Mk1 last summer - temp. hit the red, had a problem finding somewhere to pull over in a cloud of steam.

Fixed it, and it hasn't given me any issues since - I've done around 5k miles in it without it missing a beat.

[Wombat3]

General rule of thumb is you don't want to see more than 10% difference between the top & bottom results.

Did you do the test on a warm engine & with a wide open throttle & all the plugs out? If not then have another crack at it & see what you get.

If you get a cylinder reading low then stick a couple of tsp of oil in & do it again, if that fixes it then its bad rings, if not then bad valves (or a head gasket).

If you think you might have warped the head/blown the gasket then you may have oil in the coolant.

Also to test that you can use a cooling system pressure tester & see if it holds pressure and then use a thing called a block tester (buy it off ebay) which tests for exhaust gasses in the coolant.

[HeatonNorris]

I think the first check is... how is it running?

If it's running fine and there's no evidence of water / oil mixing, then why are you even doing a compression test?

[drophead]

HeatonNorris said:

I think the first check is... how is it running?

If it's running fine and there's no evidence of water / oil mixing, then why are you even doing a compression test?

Well i needed to take the cam cover off to free up some space so I thought i might as well do a compression test while everything's off. Hasn't run warm since last summer so it was a cold temp compression test.

Going to put it all back together again this weekend and re-pressurise the cooling system. If it's running like a pig and i'm having trouble with the cooling system then i'll know for sure that somethings up.

Thanks for everyone's replies.