How to tell if head gasket is blown

hu5ker555 · Post by **hu5ker555** » 27 Feb 2021, 17:47

What are the tell-tale signs of a blown head gasket on these vehicles? I've seen some videos of people opening up their coolant reservoir caps with the engine running and then it quickly boils over. Is this a reasonable test? Other things to look for?

patcal · Post by **patcal** » 27 Feb 2021, 19:28

Easiest way I know is check for bubbles in the coolant reservoir. With the car cold, carefully remove the coolant cap. Then start the car. Be careful your not too close as the coolant may shoot out if the head gasket is blown Milky color on the dipstick or oil filler cap.

Post by **SuperHerman** » 27 Feb 2021, 20:44

Free tests are looking for pressure issues in the hoses, and bubbling as described. Also looking at the coolant and oil for signs of contamination. Pulling the spark plugs and looking for clean plugs and not clean plugs. Then using a flash light to look at the piston tops for steam cleaning (meaning they should all look the same oily/dirty) - this assumes the leak is to the combustion chambers as does the spark plugs. Looking at the exhaust for white smoke. Looking for coolant loss that is not from a hose, radiator, pump, or heater core.

Compression (leak down test) test if you don't have a tester. Block gas check if you don't have a tester.

Post by **RickHaleParker** » 27 Feb 2021, 23:18

Chemical Block gas tester.

1.Tool is in the Autozone loaner program.

2. The Leak Detector Fluid is $10.00 for 8 OZ.

Post by **erikv11** » 28 Feb 2021, 08:16

The head gasket separates three chambers and the high pressure substances that go with them: lubrication (oil), cooling (coolant) and combustion (combustion gases from burnt fuel). A blown head gasket will result in mixing of two or more substances in on or more chambers. The leaks can be one-way or two-way so there are six kinds of leak, and may appear alone or in combination.

Symptoms for the six kinds of leak:
- coolant in oil (chocolate milk oil, not to be confused with thin milky layer due just to cold weather)
- oil in coolant (oily film in coolant bottle)
- combustion gases in the coolant (high pressure hoses, bubbles in reservoir, coolant gas detector tool, low compression)
- coolant in the combustion chambers (sweet smelling steam out the tail pipe, low compression)
- oil in the combustion chambers (blue smoke out the tail pipe, low compression)
- combustion gases in the oil (blown seals, low compression)

You could see one or all of these. On these engines gases in the coolant is the most common one, often seen alone.

Post by **abscate** » 01 Mar 2021, 06:33

I’m not the most experienced on head gasket work but I will pass on it is common to NOT be able to see the leak on the removed gasket, so do your tests BEFORE you pull the head

Post by **jonesg** » 01 Mar 2021, 13:06

a quick free test is remove the small overflow hose at the bottle (cap hose with a bolt or coolant will syphon out) , install a 2 foot section of spare hose on the nipple and place the other end of the spare hose in a bottle of water, with the coolant cap installed start the engine cold and watch the bubbles in the bottle, if you get a steady strong stream of bubbles that rise and fall with rpm you got a problem. You'll know within 30 seconds.

I had ordered a bottle of block tester from NAPA, by the time it arrived the 740 was gone to the junkyard, it was so obvious.

Post by **erikv11** » 01 Mar 2021, 14:49

jonesg wrote: ↑01 Mar 2021, 13:06 a quick free test is remove the small overflow hose at the bottle (cap hose with a bolt or coolant will syphon out) , install a 2 foot section of spare hose on the nipple and place the other end of the spare hose in a bottle of water, with the coolant cap installed start the engine cold and watch the bubbles in the bottle, if you get a steady strong stream of bubbles that rise and fall with rpm you got a problem. You'll know within 30 seconds.

I had ordered a bottle of block tester from NAPA, by the time it arrived the 740 was gone to the junkyard, it was so obvious.

LOL!! Yes, if you get a any bubbles at all, there is a problem! I'm not sure you need to try a bucket to see those but this method would catch it without the hassle of a combustion gas detector I agree. However there are much more subtle fume leaks that are also problematic.

You can "rent" the block leak detector from most auto parts stores too, although you must buy the fluid.

Post by **jonesg** » 01 Mar 2021, 18:38

erikv11 wrote: ↑01 Mar 2021, 14:49
jonesg wrote: ↑01 Mar 2021, 13:06 a quick free test is remove the small overflow hose at the bottle (cap hose with a bolt or coolant will syphon out) , install a 2 foot section of spare hose on the nipple and place the other end of the spare hose in a bottle of water, with the coolant cap installed start the engine cold and watch the bubbles in the bottle, if you get a steady strong stream of bubbles that rise and fall with rpm you got a problem. You'll know within 30 seconds.

I had ordered a bottle of block tester from NAPA, by the time it arrived the 740 was gone to the junkyard, it was so obvious.
LOL!! Yes, if you get a any bubbles at all, there is a problem! I'm not sure you need to try a bucket to see those but this method would catch it without the hassle of a combustion gas detector I agree. However there are much more subtle fume leaks that are also problematic.

You can "rent" the block leak detector from most auto parts stores too, although you must buy the fluid.

I had observed the subtle "other" signs already, coolant on spark plugs was a clue. !
Just wish I still had that car today, the red block engine was so simple to wrench on compared to this 5 cyl.