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What test is better at detecting a blown head gasket, a compression test or a cylinder leakdown test and why?
Best way to Test for a Blown Headgasket
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No need for the leakdown test. That is for valves or rings that are worn. A compression test will tell you and quick! :smoke:
You cannot tell by water in the oil or water out the tail pipe, etc. For instance, the most common place a small block Ford will blow is between the piston bores. No water jacket is there. Loss of power and running a tad warmer are the symptoms.
You cannot tell by water in the oil or water out the tail pipe, etc. For instance, the most common place a small block Ford will blow is between the piston bores. No water jacket is there. Loss of power and running a tad warmer are the symptoms.
I have to disagree about the leak down test. This is why, with the engine warm a leak down test would create air bubbles in the cooling system when a gasket is blown. The bubbles would appear in the radiator with the cap off. hissing from the oil fill tells you you have a blown gasket into the oil galley or bad rings
A leak down tester is a great tool! If you hear hissing though the throttle body, you have a bad intake valve. Hissing out the exhaust, you have a bad exhaust valve. Hissing through the oil cap, you have a blown gasket into the oil galley, and air bubbles in the radiator, you have a blown gasket into the cooling system.
A chemical test at the radiator will tell you if you have a blown gasket into the cooling system too.
A leak down tester is a great tool! If you hear hissing though the throttle body, you have a bad intake valve. Hissing out the exhaust, you have a bad exhaust valve. Hissing through the oil cap, you have a blown gasket into the oil galley, and air bubbles in the radiator, you have a blown gasket into the cooling system.
A chemical test at the radiator will tell you if you have a blown gasket into the cooling system too.
Not necessarily. I've done plenty of compression tests that have come out just fine on the compression. It wasn't until I performed a chemical test at the radiator or a leak down test that the head gasket showed it's dark side.Tominator said:If it's blown, low compression is the result. It may not be blown at the water jacket or near an oil gallery, but WILL result in low compression on one or more cylinders.
My own turbo Mustang had great compression. A week later it popped its gasket. After tearing it down, we found that it had been blown for awhile into the lifter galley. Major burn marks on the back side of the head ports.
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Well we suspect it on my girlfriends mustang.
Now what exactly is a blown headgasket? I know there are 2 surfaces of the gasket, does it blow in the middle or soemthing?
Also how would a compression test isolate it? How would you know it was the gasket that was the problem and not something else? Also doing the leakdown test, if it blows out the oil cap, would that also mean possibly bad rings?
Now what exactly is a blown headgasket? I know there are 2 surfaces of the gasket, does it blow in the middle or soemthing?
Also how would a compression test isolate it? How would you know it was the gasket that was the problem and not something else? Also doing the leakdown test, if it blows out the oil cap, would that also mean possibly bad rings?
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Agree 100%, we forget that a head gasket failure has different severity stages and, assume all have to be identical. The important thing, is that there are tools, tests and procedures that need to be combined as confirmation methods some of the times.JUSTNLX said:
A chem test is done at the radiator. A clear tube with a seal is placed around the radiator cap opening. A blue chem is added to the tube. I'm not sure what the chem is. As the engine runs with this tube/chem on the radiator, air bubbles go through the tube/chem from the radiator. If combustion gases are present, the blue chem will turn yellow/clear.Tominator said:
Do not let coolant into the tube/chem. It will destroy the chem.
This will only detect a gasket blown between the combustion chamber and the cooling system.
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I know you will lose compression, but what exactly happens when it blows?Tominator said:
I dont mean what are the side effects of when it blows, but what happens to the gasket when it blows?
Also to the one who asked if I was having problems, yes my girlfriend and I suspected it on her mustang.
When you say you suspect this, what makes you suspect a blown head gasket? If you are talking about a 3.8, especially 94-98, then chances are, the gasket is bad. In the 3.8, most likely one of the two front cylinders.
A blown head gasket can manifest itself many different ways - most commonly a coolant leaks into a cylinder. Signs of this would be White Smoke out the tailpipe in extreme cases, loss of compression, loss of coolant with no extrenal leak, extremely clean (steam-cleaned) spark plug from the affetced cylinder.
You could also lose oil either into the engine or externally. This will not last long, and the ticking noise from the offending side's valvetrain will become increasingly annoying.
To find a blown gasket, and zero in on the cause will take a few steps. First, a compression test will tell you that there is a problem. (Be wary of two side-by-side cylinders with the exact same compression - could blow the gasket between two cylinders.) When you do the compression test, look at tyour plugs - if they are wet, look extremely clean, or even have oil fouling, indicate problems.
A leak down test will narrow it down and tell you where it is leaking - like was said above, listen for hiss in valve covers, exhaust, bubbles in radiator, etc.
If you get bubbles into the radiator, do a pressure test on the cooling system and see if it will hold pressure. If will not hold, and you cannot find any external leaks, probably the head gasket. I have seen blown gasket that would hold cooling pressure when cold, but leak when cold, though.
Lastly, go to a parts store and get a chemical test to verify the head gasket is leaking inot the cooling system.
A blown head gasket can manifest itself many different ways - most commonly a coolant leaks into a cylinder. Signs of this would be White Smoke out the tailpipe in extreme cases, loss of compression, loss of coolant with no extrenal leak, extremely clean (steam-cleaned) spark plug from the affetced cylinder.
You could also lose oil either into the engine or externally. This will not last long, and the ticking noise from the offending side's valvetrain will become increasingly annoying.
To find a blown gasket, and zero in on the cause will take a few steps. First, a compression test will tell you that there is a problem. (Be wary of two side-by-side cylinders with the exact same compression - could blow the gasket between two cylinders.) When you do the compression test, look at tyour plugs - if they are wet, look extremely clean, or even have oil fouling, indicate problems.
A leak down test will narrow it down and tell you where it is leaking - like was said above, listen for hiss in valve covers, exhaust, bubbles in radiator, etc.
If you get bubbles into the radiator, do a pressure test on the cooling system and see if it will hold pressure. If will not hold, and you cannot find any external leaks, probably the head gasket. I have seen blown gasket that would hold cooling pressure when cold, but leak when cold, though.
Lastly, go to a parts store and get a chemical test to verify the head gasket is leaking inot the cooling system.
typical symptoms of a blown head gasket may include: bubbles of air coming up into your radiator (remove cap before starting), leaking radiator, milkshake colored oil, overheating, rough running, coolant or oil running from head, spark plug(s) that have a green tint (if green coolant), white colored or sweet smelling exhaust.
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