Carnut68

94 pickup with 22RE with 160k miles but maybe 10-15k on replacement engine (not done by me). Idles smoothly (after exhaust replacement which cured bouncing idle due apparently to a leak near the 02 sensor) but pressure builds up in the coolant system which causes it to blow out the expansion hose. If I put a large coolant funnel on the radiator spout, once the truck warms up coolant gets pushed up into the funnel to the point where there is probably a quart or two. Meanwhile the idle starts climbing. Eventually bubbles will come up and it will drain back down into the rad and the idle goes back to normal. I can also squeeze the upper rad hose which will cause it to suck the coolant back in. I have used a fluid block tester but the results are inconclusive. Can this be a really hard to burp blockage somewhere? I have parked it on an incline and attempted to burp it but this just keeps happening. I just got the truck running again and am really not excited about doing a head gasket so I am hoping there is another possibility.

Co_94_PU

iTrader: (-1)

Please explain how you determined "inconclusive"

Carnut68

The test fruid did not change from blue to yellow, more like a bluish green. Maybe I didn't do it completely right or maybe I just suck with colors.

Co_94_PU

iTrader: (-1)

Yellow and blue make green. Basicly if it reacts at all it found something. Given enough time and gas it will turn completely.

the_supernerd

If you think the green coolant is making it difficult to see the color change, you can flush it real good with distilled water to get rid of the green and test it again. Another solution is to get someone with an exhaust sniffer to see if there are hydrocarbons coming out of the radiator. A pressure test on the cooling system might also help.

Co_94_PU

iTrader: (-1)

Oh I didn't even connect yellow/green coolant contamination of the test fluid, I can see that being a little inconclusive now. You could use a catch can to ensure you're only getting gasses and not fluid, but it's maybe easier to just drain and refill the system with water.

Jimkola

The block tester methods and results on the 22R were debated bitd at our place. A few techs were frequently condemning headgaskets, even if that wasn't the reason the vehicle was brought in for service.
Watching them run the test we concluded that they were leaving the testing cylinder in the radiator neck too long and were getting false positives for the presence of exhaust gas. A hard failure would change the fluid from blue to yellow after only 1-2 pumps of the bulb, but still, you should see a color change within a minute or two. They were leaving the cylinder in the neck for 5+ min.
Water/coolant from the radiator should never enter the testing cylinder. if that happens you need to stop the test, lower the water level in the radiator, cleaning the testing cylinder very well and run the test again.
Going from deep blue to med. green would be inconclusive. Medium green could be indicative of exhaust gas, but at such a minute level it's doubtful the driver would notice drive-ability issues, I'd think they're more more likely to see a coolant reservoir going empty after several days of driving. Maybe a very faint "miss". In those inconclusive test cases we'd flush the system and run a second test. If still undecided we'd move to a leak down test.

One of our techs used to use the smog machine to test for exhaust gas at the radiator. Then one day he accidentally sucked coolant into the probe and it got pulled into the machine's analyzer. After paying the Bear Corp a few thousand dollars to fix the smog machine the tech agreed to use the slightly slower block tester.