compression check on 77 merc 470 :(

[CAPTKEV85]

today i did a compression check on my wonderful 470. i let the engine come up to operating temp. then shut it down and pulled number 1 plug. put tester in cranked engine. psi was 130. check #2 psi 130 checked #3 115 checked #4 130. so obviously #3 is a problem to my overheating and air getting into my cooling system. ohh when i do test run the overflow bottle fills up and spills out. but when she cools it does not suck the antifreeze back in. resulting in now antifreeze in engine. i have put a 1/4 of gallon of coolant in. i think my head is bad. is this possible? is there any other test i can preform? she runs great but when i go full throttle she spits antifreeze everywere. no coolant in oil, or in cylinders. input please:redface:

 

[CAPTKEV85]

Re: compression check on 77 merc 470

owe and when the engine was off there was a constant little bubbles in the overflow bottle for a minute after shutdown. engine was at operating temp not overheating.

 

[Don S]

Re: compression check on 77 merc 470

115 to 130 is not a compression problem. What did the spark plugs look like, any of them look like new?
You can always drain the coolant out of the system and do a pressure check and see if it holds air pressure (YES, you have to drain the antifreeze)
PS: 470's are noted for head gasket leaks. It's that wonderful open deck design and aluminum block and cast iron head. What could possibly go wrong.

 

[abj87]

Re: compression check on 77 merc 470

Seems like a head gasket problem. Pull the head and see what's up. Those bubbles you see are exaust gases in the cooling system.

 

[CAPTKEV85]

Re: compression check on 77 merc 470

THE plugs are orig from april of this year . i have never seen plugs so clean in my life. thats y im confused. this motor runs mint no hesitation backfiring missing,stalling, nothing. but the air in the coolant is a big prob. #3 cylinder i testes at 115 psi on the 3rd test the first test was around 108 is that still an issue. all the other cylinders are dead on but #3.

 

[Firestar]

Re: compression check on 77 merc 470

Head gasket.

 

[JustJason]

Re: compression check on 77 merc 470

well.....
If your unsure or concerned about compression test readings...
Then the next step is leakdown testing to figure out where that compression is going.
Not much else in between.
If compression is your concern....
Do a leakdown.

 

[CAPTKEV85]

Re: compression check on 77 merc 470

LEAKDOWN TESTER never down it before. something i can purchase at auto store. or do i have to use and air compressor.

 

[CAPTKEV85]

Re: compression check on 77 merc 470

is it safe to rule out my exhaust manifold being cracked. because noone makes my style manifold anymore.

 

[abj87]

Re: compression check on 77 merc 470

Double post please remove..damn blackberry!

 

[abj87]

Re: compression check on 77 merc 470

A leak down test won't tell you much more that what you already know that one cylinder is loosing compression. Don't waste your time with more tests and pull the head. I'm almost willing to bet money that its a head gasket.

 

[JustJason]

Re: compression check on 77 merc 470

Don't waste your time

if i only had a nickel.........

 

[ne7800]

Re: compression check on 77 merc 470

there is a tester that can test for exhaust gasses in your coolent if there is exhaust gasses in there then you need to pull the head

 

[CAPTKEV85]

Re: compression check on 77 merc 470

I'm pretty sure myself that its the head or the gasket. im justing trying to rule stuff out. because this engine model is becoming endangered, and parts are not avail, anymore. ive just never seen a motor run like a champ with no signs of probles. well exept the gyser of antifreeze after a half hour of running at full throttle. well thanks guys for the help.