I have been confused a bit about my coolant. Some mornings the overflow tank has above max fluid and coolant is low in the radiator. I top it off with 1/4 or 1/2 cup of coolant. A couple of times before I started checking daily I had seen the temp rise fall in a cycle and so I would stop the car, let it cool down and then find the coolant needing a top off. I burp the system. I've used Mazda method of reving it for 5 min a couple of times and I have also used that big **s funnel method. I still find I need to top off just a tad each morning, although for the past 4 mornings there is no extra in the overflow tanks and only a 1/4 cup or so down.

Anyway, I am replacing a few soft hoses and connectors as I did have a couple burst on me recently. 188K miles on all these parts. Since the head gasket often comes up when searching this kind of air leak problem, this morning I did a compression test. I got 170-180psi on all cylinders dry (fuel injector connectors disconnected). With a touch of oil dropped in there, I get 180+ on all cylinders.

My question for this thread is, do these measurements tell me my head gasket is fine and my air leak is elsewhere? I am searching other sources for air leaks, of course and there are some threads on that. I would put that in a different thread as I continue to search, so I don't want to ask about it on this thread. I just want to know about these compression measurements in regard to head gasket health. I was happy to see these measurements, but don't want to make a conclusion about the head gasket without asking around.

The long explanation at the beginning is just to let people know how I came to decide to do a compression test.

Thanks for any input you can provide.

Stefano
Concord, CA

 

Unfortunately a simple compression test doesn't rule out a headgasket issue.

Pressure test the cooling system both when hot & cold, check for leaks. Also remove sparkplugs, leave it pressurized for 1\2 hr, crank the engine over with the starter, see if any coolant is ejected from the cylinders.

Next test is a combustion gas detection test, which requires a special tester. Example TK tester.

 

Thanks for the input. I have also heard from other sources that a leak down test should also accompany a compression test.
I have most of the parts needed for a leak down test without having to buy a complete kit. I am just waiting on a brass
tee of the right fittings and I can do that.

I have the combustion gas tester as above, but cannot get a good reading as the coolant just rises into the tester and mixes
with the blue dye.

If the leak down test is inconclusive, I may just have a mechanic perform the pressure test on the cooling system. I don't
want to keep buying testing kits. Unless there is a fitting available for the radiator inlet and I can use my own compressor
and my various fittings.

I do have an old radiator cap, though. Maybe I can adapt it somehow to accept a fitting on top.

 

Compression verifies compression but not necessarily a blown head gasket because it does depend on where the break is and also it may be a cracked head.
Leak down confirms suspicion low or uneven compression.
Cooling system test will check and confirm a seal cooling system. But not necessarily a blown head gasket if it is a heat expanding break or crack in the head.
The chemical cooing system check will confirm exhaust gases in the cooling system which means a cracked head or blown head gasket.
None of these technically will confirm a cracked head but if any are negative when you pull the head you should have it pressure tested.
If you are getting coolant back in the testing tube, then you may re-read how to do it or watch a video. I would guess more than half the DIY using them have the same compliant you did. But if the cause of the coolant pushing back up the test tube it is an indication that the engine is pushing leaked pressure in the cooling system which is a blown head gasket or cracked head.