Block test for head gasket- how reliable?

[LCWannabe]

Hi, I have no real reason to suspect my head gasket is bad other than reading about HG issues here. My 96 has about 215K on it now. I rented the block tester from Autozone and the dye never changed color at all. Is this a reliable indicator that my HG is solid?

The test involves sucking air from the cooling system through a blue dye. If the dye turns yellow, there are emission particulates in the cooling system, indicating a leaking HG.

 

[KLF]

That would only tell you if combustion gasses are leaking into the coolant. A failed HG will present itself in many ways, sometimes just as an external leak down the side of the block, nothing more.

I would also try to do a leakdown test.

 

[LCWannabe]

Well, I don't think I'm losing coolant, just trying to ensure I don't need to worry about it. Does the pic show any indication of precious work at all?

 

[scrowley]

The external leak is usually in the back of the motor...cylinder 6. pass side. Take a inspection mirror and flashlight and give it a look.

You can also send your oil out for analysis at Blackstone lab. They will tell you the condition of your engine along with HG

 

[airsix]

I used the Autozone block test and got a false negative. I drove another 30 miles or so and the other signs convinced me to tear it down. Sure enough my #6 was blown out.

 

[thatcabledude]

Well, I don't think I'm losing coolant, just trying to ensure I don't need to worry about it. Does the pic show any indication of precious work at all?

View attachment 804247

That RTV job doesn't look stock to me..... Maybe work has been done. Who knows?? Only the PO, maybe.

 

[LCWannabe]

Cabledude- that's what I was wondering about. It does have an aftermarket radiator too- maybe an indication that the HG was done at some time? Bought it from a dealer and very little prior history on it. I don't think I have any symptoms of leaky HG, but the Mud has me a bit worried about it.

 

[thatcabledude]

If it isn't showing any symptoms I wouldn't get hung up on it.

Your throttle cable in that pic on the other hand.....

 

[robertaleon]

If you don't have any real symptoms , as others have said don't worry too much at this point. The block test you mentioned is reliable but must be paired with several other diagnostic tests. I had a replacement radiator on mine and things were fine except for a cracked lower tank and loosing fluid. Replaced with a Koyo , performed a cooling system overhaul with hoses and tstat and things were good for 9 months. Then I was boiling over at freeway speeds. Tested tstat and water pump, and coolant flush but still didn't fix it. Found sludge (aka peanut butter) on rad cap and bottom of overflow bottle, seep from drivers side block-head between #3 and #4, leak down test failed, compression test failed and block test failed plus sweet smell from exhaust. That's when I knew for sure I had an HG problem.

The sealant on the half moons does not look OEM and as mentioned before that throttle cable has seen better days.

 

[OG 91 LC]

There are two sides that come up with the HG issue. The people on the PM side of this issue and the people that will not replace the HG until it blows. I'm in the process of getting mine dialed. New hoses. New belts. New radiator. All OEM. Thinking about a new water pump and fan clutch. After all that I will add a scanguage unit. What led to this???? A HG leak after I flushed the block. And I was tired of wondering "what if" every time I drove it. I was tired of looking at my temp gauge every time I drove it. It takes $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$!!
But now I get to enjoy my truck.

 

[LCWannabe]

Throttle cable is on the list guys. HG is probably on the list too- at some time. On the other hand, the HG job would be my hardest mechanical job to date and if it is not needed its not needed. My problem is deciding if it's needed. All advice welcome!