possible head gasket 95 El Dorado

[outdoorsy]

I am new to the forum, I bought the most beautiful 95 El Dorado with 126k on it. I got a great deal on it and assumed that it has a blown head gasket. I am continuing to get bubbles into the overflow tank and of course it overheats after a short while. I did run the exhaust gas test blue liquid at the radiator over flow tank for several minutes and it never turns yellow. I am going to try this test again to make sure i did not contaminate the test. I have read that someone said something about a purge tube or something regarding the bubbles. Not sure where that is, but i will locate it. I did pull plugs and run the car and it seems like the bubbles did slow down when a few of the plugs were pulled. But it just does not add up that i don't see exhaust gases in the dye test. Thankful, but just don't understand these amazing motors. I come to the experts asking for advice on this beautiful car.

[KHE]

Disconnect the purge line from the surge tank. Start the engine and there should be a steady stream of coolant flowing from the purge line. If not, find out what is clogging the purge line.

[outdoorsy]

I did check the purge line going into the top of the overflow tank, it has flow at an idle.

[JohnnyG]

So are the bubbles you are seeing coming from the purge line or somewhere else?

Couple of things to watch out for on this test.

Make sure the test fluid in the kit is fresh and not passed any expiration date.

Make sure the test fluid has not been contaminated by someone else.

Make sure nobody has recently flushed the coolant system or changed the coolant.

Make sure any recent additions to the coolant to adjust the level have been very small.

Make sure the cap on the reservoir is tight and not leaking.

Make sure the pressure rating of the cap is correct and not failed.

Make sure the seal from the sampler to the tank is not leaking air, you want it to sample what's in the bubbles you are seeing. (No peeking)

Finally make sure the vapors above the coolant in the reservoir are representative of what is normal operation, in other words, that no fresh air has gotten in after an overheat episode.

[outdoorsy]

Re-checked the purge line and identified that there are in fact bubbles coming from the purge line.

Make sure the test fluid in the kit is fresh and not passed any expiration date. I did not see a expiration date on the fluid and was told previously that it can be reused over and over as long as it was not contaminated by antifreeze or any other foreign substance. i always dump the results anyways.

Make sure the test fluid has not been contaminated by someone else. Just me using it.

Make sure nobody has recently flushed the coolant system or changed the coolant. The coolant systems is constantly being added to due to it bubbling out while testing.

Make sure any recent additions to the coolant to adjust the level have been very small. They are cups of water at a time, sometimes more. Usually after it cools down.

Make sure the cap on the reservoir is tight and not leaking. I have tried multiple caps, and they all hold pressure until it hits that 243 mark or when the car says idle engine.

Make sure the pressure rating of the cap is correct and not failed. multiple caps tried.

Make sure the seal from the sampler to the tank is not leaking air, you want it to sample what's in the bubbles you are seeing. (No peeking) Using these samplers they have an angled plug that fits snuggly into the radiator cap outlet. you make sure that the coolant level is lower to allow for the tester to seat deep enough to not pull up coolant into the test fluid. I then connect to vacuum line and it starts to pull those bubbles up through the fluid. I have used this test on several cars and it works well. However after 2 different tests on this Northstar engine it stumps me.

Finally make sure the vapors above the coolant in the reservoir are representative of what is normal operation, in other words, that no fresh air has gotten in after an overheat episode. i can control the fresh air for this test at the radiator cap, however i am unable to tell if it is being introduced somewhere else in the system.

I appreciated your ideas and troubleshooting. Thanks

[JohnnyG]

OK, time to test the test kit. This also applies to rockfangd. Test some vapors that are KNOWN to contain exhaust gasses.......like the exhaust pipe of a running engine. If in fact the fluid can be used repeatedly, you won't be out anything.

I often wonder why a CO detector can't be used for this test. I sometimes test CO detectors with auto exhaust gasses, the results are usually immediate and repeatable. I understand that there are other components that make up the bubbles, but this would certainly rule out good clean air.

[KevinW]

OK, time to test the test kit. This also applies to rockfangd. Test some vapors that are KNOWN to contain exhaust gasses.......like the exhaust pipe of a running engine. If in fact the fluid can be used repeatedly, you won't be out anything.

I often wonder why a CO detector can't be used for this test. I sometimes test CO detectors with auto exhaust gasses, the results are usually immediate and repeatable. I understand that there are other components that make up the bubbles, but this would certainly rule out good clean air.

A key factor would be using untreated exhaust gas to verify a test solution colour transition, possibly after the recommended procedure has failed to produce any results. Exhaust passing through a cold or non-functioning catalyst will easily have over 500 PPM CO. Combustion where oxygen is the limiting reagent is conducive to the production of high levels of carbon monoxide. Exhaust sampled shortly after a cold start would be best; smoldering newspaper is a also good source, and who knows, a lit cigarette may yield enough to cause the solution to change colour. I measured over 20 PPM on the breath of someone who had finished their cigarette 10 minutes before!