Inliners International Forums General Discussion Engines Chevy 250 compression

Hi can someone please tell me what a good compression should be for a chevy 250? Im not sure what the mileage is on the motor. We tested cylinders 5 and 6 yesterday. 5 gave us 120 and 6 was about 150. That was on the engine cold. I'm noticing a small antifreeze leak just under my torque converter and im not sure if it's a freeze plug or something else. But my temp is pretty high. I have a 180 thermostat but the gauge is reading about 210 to 220. Any thoughts?

It's generally between 15 and 20 psi per static CR, so for 8:1 120-160. Test: engine up to full temperature, throttle and choke full open, same number of turns on the starter.
Important: less than 10% difference between best and worst.

High temp all the time? Traffic only?

It actually overheats just idling in the driveway.

I will run that test and see what I get at warm temperature. Thank you.

Does the fan have a shroud?
Have you tried comparing your gauge with a candy thermometer?

Panic my fan does not have a shroud. And Im still using my stock fan. I haven't tried anything else other than my gauge.

I hesitate to say the missing shroud is your problem, but it doesn't help. The lower the vehicle speed the more the fan relies on the shroud to force air to pass through (not around) the radiator core.
How old is your water pump? AFAYK are your pulley sizes stock?

So the motor is fully stocked. The only thing i have done it's split the manifold. The water pump is probably a couple of years old, but I drive my car maybe 5 times a year. I know not enough lol. It's mostly a show car and occasionally drive it in town for pleasure. I do see a little movement back and forward from the fan when it's running. Almost like my pulley is loose but it isn't. Is that an indication of a bad water pump?

My next thought is a build up of rust, old gaskets, etc. in the radiator and/or water jacket in the engine.
Sometimes this can be improved by simply knocking out the core plugs and scraping up inside the block.

Check your timing. The vacuum can could be bad and not giving additional timing at cruise and idle. This can also cause high engine temps.

If the car is running rich, can that cause high temps? I noticed both 5 and 6 plugs were really black.

No.
Black and wet or dry?

Black and dried.

I ended up doing the compression on all cylinders and I got 150 on number 6, 120 on 5,4,3,2 and 110 on number 1. This was with the engine cold.

I think it is common to have lower compression on cylinder one. Right next to the water pump and thin cylinder wall contributes to greater wear on cylinder one. I believe.

Why you have high compression on cylinder six I can't explain. Possible camshaft wear closing the intake valve too early?