I recently bought my 84 GSL and did a compression check on the engine about 3-4 weeks ago. The motor was completely cold. I used a "boinger" compression tester with a check valve in the base.

The compression reading maxed out at about 95 psi on both rotors. When I pulled the gauge off I could feel three even pulses per rotor. The engine has roughly 140K miles and is totally stock (as far as I can tell).

This morning I was doing some other stuff, such as cleaning up my rat's nest removal, and decided to do a hot compression check. I had driven the car to normal operating temps about 5 minutes beforehand.

The reading never got higher than 80-ish psi. Still have even pulses on both rotors, though.

My questions are: Is this a cause for concern? Should the reading go back up to 95 psi on a cold motor, or should I expect bad things? Could some ATF help bring up the compresson?

Any ideas, suggestions, comments, etc. are welcome.

 

It sounds like the engine is fine. I have seen engines in the 50's run fine for years. Make sure when you are testing to open the butterfly plates, this gives you the correct reading. Don't put in any ATF or do anything but drive it and keep it tuned up. The best thing you can do is change the oil every 2000 miles like clock work. On turbo or supercharged motors 1000-1500 miles.

 

First: cold compressiontests are worthless,

Second: try to get a decent (digital) compression test done if you want to get accurate numbers (digital even recalculate to 250 Rpm Mazda specs)

Compression numbers are not holy, if the car starts fine in cold an hot condition, you're fine. I've got people driving with 5 Bar for years now, only if you want to do some mods for more power you should be carefull..... It's just a sign that the engine has milage on it, it's not a garantee your seals won't break.
The lower the compression, the more you need to prep yourself for a rebuild, but there's no ETA given on it

 

Thanks.

I doubt I will waste the time or money to get a digital test done. I don't plan on modding the motor whatsoever, other than the rat's nest removal, air pump and catalyst deletion.

The car starts "fine". It doesn't fire up vigorously, but rather starts in a slow "putt-putt" fashion to a normal idle. My most annoying problem right now is a rather prominent misfire at idle. The plug wires looks a bit old and may need replacing. I am thinking about fashioning a direct fire setup that seems to be so popular with the DIY'ers around here.

I was just concerned the engine may not be long for this world.

If I were to sell this engine to someone, with transmission, how much do you think it would be worth?