While trouble shooting a high oil pressure problem I found the radiator fluid is a little foamy so figured I had better do a compression test and make sure the head gasket is ok.

I have the correct gauge but it is one that needs to be pressed and held into the sparkplug fitting instead of a screw in one. Which makes it difficult to hold the throttle open and start the car.

I have a wire set with a remote contact for starting the car from the engine compartment but I do not know which terminals on the battery\solenoid to hook it up to, if anyone can help with this that would be great!


TLDR:
Using a contactor to start the car while troubleshooting engine, dont know what posts to hook it to.

 

I cant figure out how to edit the thread but it is a 66 Mustang, 289, everything is pretty much stock except for an electric fan.

 

You do not start the engine to do a compression test. You pull all the spark plugs, and you make a measurement. Using a remote starter, crank the engine over 5-6 times or until the gauge stops moving and record the value.

If you have a cracked head or head gasket problem you may not find it with a compression test. There is a special test fluid and tester you use to see if your anti-freeze has hydrocarbons in it.

 

Yep, what JLG said above. Don't know where you live in Wa. but if you can't find the hydrocarbon tester near you, then try & get a leak down tester. It works similar to a comp test, but it will actually show you the percentage of leakage in each cylinder & also localize exactly which cylinder is leaking, as opposed to the hydrocarbon checker which will only tell you that you have a leak, (which you already know due to the bubbles) but won't tell you where it is.

 

You can also get a pressure test done of the cooling system. The tester will apply 12 psi or so to the system. If it leaks down, it could be bad gaskets, cracks, bad hoses, or the tester installed improperly. But it should hold 12 psi or so for 10 minutes or more.

The tester runs about $100 if you're into buying tools like I am. A differential compression tester will run about the same $$. If you don't want to buy them, call around the auto parts houses; they might have one they can loan you. Or just pay a shop to get the tests done (personally, I don't trust letting a shop do these tests for me unless I can watch because they also have an interest in the repairs. Yeah, I know, they're in business to fix cars but I prefer to do as much work as possible myself to avoid these worries.)

 

I may be stupid when it comes to this as I've never done it but how could you possibly hold it with enough pressure by hand to do a compression test?

 

It's actually not as hard as you might think, if you have good access to the plug hole. That's the kind we had when we were young and we used it a lot.

But it really takes 2 people when using that kind of compression gauge. One to hold it in the plug hole, the other to crank the motor.