Tonight I bought a fancy new cooling system tester after noticing I was loosing coolant. I hooked it up to the radiator and topped the coolant off, and pumped it up to 15psi. The gauge showed that I lost a few pounds in a couple minutes, but I did not find any external leaks. I reset the gauge and started up the car. The gauge was not really building pressure, so I pumped it up to about 15psi again. From there it steadily rose to almost 30psi before I shut it off. what is this telling me?

Pick one or more:

A. The tester is junk
B. You don't know how to use the tester
C. Your radiator cap is defective
D. There is a head-gasket leak

If your tester is accurate you pretty much have to pick C, because it should not hold 30 lbs. ever.

[This message has been edited by Gall757 (edited 11-20-2014).]

The radiator cap was replaced with the test cap during the test..

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Red '84, 75,000 miles.. work in progress

OH......

well then we are looking at 'D' I think.....a leak from a cylinder to the coolant.

That's what I was afraid of, does anyone know of any shops in Dubuque, IA that can check for cracks in the head?

Although a PITA, you can remove the spark plugs when running the test to see if pressure drops more quickly. Without them helping hold pressure, head gasket leaks will have far less of an issue leaking into the cylinders and you'll see that on the gauge.

Any half-decent machine shop can check heads - you just gotta pull them off and drop them at a shop. Some auto parts stores have attached machine shops, but I personally try to find the old grumbly guy whose been doing it for years.

So is a L4?

Try Pull spark plugs.
Example:
If 4 plug shows "rust" then could be dead intake manifold gasket.
#4 under vacuum and coolant is 0-16 psi... Is easy for #4 sucks coolant from bad/loose gasket.
Intake Man Gasket w/ bad install can easily die.
This gasket isn't used w/ any sealer. Many people use RTV and is a big no.
low torque is big problem.
over torque can break intake.

Fixing if true?
use FelPro gasket and torque to spec. (25 ft/lb)
Torque is for clean and dry hardware but be careful because 1 goes thru head into oil drain hole for valves. torque to spec that bolt can break intake.
(1 hole next to dog bone bracket for 87+ versions. Not sure if applies to older versions. Very likely is same.)

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

[This message has been edited by theogre (edited 11-21-2014).]

Good idea, will try that as well. Yes 4 cylinder w/ 77,000 mi.