compression test procedure

[kmongar]

1995 VP 5.0FL SX Cobra (OMC Ford 302); starts and runs OK

The VP engine manual says to "run engine up to normal operating temperature" to do a compression test.

A Mercruiser service bulletin (97-25) says to do the test "with the engine at normal room temperature."

Question 1: Which is correct? cold or hot?

Question 2: If the test can be done on a cold engine...is it OK to do it with the exhaust manifolds removed?

I will have the manifolds off for replacement and it would be far easier to do this test without them installed. Access to the plugs and plug holes is pretty tough on this Ford set-up.

thanks

 

[Bt Doctur]

Re: compression test procedure

pull all the plugs, lock throttle plate full open, ground hi-tension lead from dist or remove the positive side wire(s),use a fully charged battery and spin motor atleast 3 revoloutions.record all readings. all should be 10-15% of each other

 

[achris]

Re: compression test procedure

Run the engine to normal operating temperature, pull all plugs, open throttle fully(and leave it open), ground coil HT lead, crank engine a few times to clear excess fuel from opening the throttle. With the compression gauge in each plug hole, crank engine for 3-4 revs. No greater variation between readings of 20psi.

Chris............

 

[Bondo]

Re: compression test procedure

I will have the manifolds off for replacement and it would be far easier to do this test without them installed. Access to the plugs and plug holes is pretty tough on this Ford set-up.

Ayuh,..........

A Compression Test done in the fashion stated above,......
Even on a Stone Cold motor will give you readings that are Very Acceptable,....
For determining the current Health of your motor.........

If you discover an Issue,.......
Throw it back together,+ do a Hot engine test........

 

[Robj]

Re: compression test procedure

I just do mine with a cold engine. Not when it is 0 degrees, but 60 degrees F or more is O.K. in my book.

Have a great day,

Rob.

 

[njlarry]

Re: compression test procedure

IMHO you'll use a lot less burn medication on your fingers with a "room temp" engine. As Bondo suggests, you can do a warmed engine test later. Most do it at normal ambiant temps.

 

[JustJason]

Re: compression test procedure

how many times do we go over this????

 

[a70eliminator]

Re: compression test procedure

Well, nobody answered his #2 question about the manifolds being removed. The answer is: No, the exhaust manifolds do not have to be on the motor to perform the test, it will not effect the pressure readings.