I have a junk yard motor in my truck since I cracked a piston in my original motor. It's been running ok up until the last couple days. The odd time there was coolant on the ground but I never inspected too closely because I haven't had time.

Today I was driving along the highway when all of the sudden, no heat at all and temperature gage on the dash went down to cold and the boost came up. A couple minutes later the heat came back and at the same time the temp gage came back to normal.

I drove it home and again the last few miles I had no heat and temp gage back to cold. I drove it in the garage and the first thing I noticed was the hose going to the heater core dripping where the rubber hose meets the plastic fitting at the firewall. The upper rad hose is rock hard and the whole system appears to be under lots of pressure. I don't dare take the overflow tank cap off.

I am thinking the head gasket is leaking and over pressurizing the cooling system and creating air locks in the system. Does that sound about right?

I don't want to change the head gaskets without being sure. I am sure kicking myself for not pulling the heads when I had the motor out of the truck. I was hoping it would last long enough that I could afford to build my original motor. That is a few months away from even being started.

So let's hear some theories on what is going on and how do I diagnose it?

It has all the common signs of a headgasket failure thats for sure.

What gets me is why do I have no heat and no temp gage? Where is the sensor for the temp gage?

I posted this in the wrong section can some please move to the 04.5-05 LLY section?

Read my recent events here http://www.dieselplace.com/forum/showthread.php?t=273713

It was a head gasket.

Did you notice no heat and temp gage going down to nothing?

Ahh ****.... I guess I'm going to have to fix my old motor and swap it back in. Sounds like less work then doing the gaskets in the truck. I'm getting sick of this thing. Maybe time to send it down the road.

What gets me is why do I have no heat and no temp gage? Where is the sensor for the temp gage?

low on coolant? Sensor is located next to the thermostats:)

If you lost enough coolant it could be showing air tamp not coolant temp???

low on coolant? Sensor is located next to the thermostats:)

If you lost enough coolant it could be showing air tamp not coolant temp???

Wierd thing is that I cracked the bleader on the thermostat housing and coolant came out. Pretty wierd it would blow ice cold air instantly and temp gage drops to cold at the exact same time. The sensor gage has alway read lower then it used to right from the start. I always wondered if it was a bad sensor.

It's -20 here right now so when it starts acting up it blows coooold air quickly.

low on coolant? Sensor is located next to the thermostats:)

If you lost enough coolant it could be showing air tamp not coolant temp???

Coolant tank is maybe even a bit overfull and i hear and see it surging back in after shut down. Seems like air escaping perhaps. Perhaps I had a vapour lock but I am pretty sure there is too much pressure in there too.

Did you notice no heat and temp gage going down to nothing?

Ahh ****.... I guess I'm going to have to fix my old motor and swap it back in. Sounds like less work then doing the gaskets in the truck. I'm getting sick of this thing. Maybe time to send it down the road.

Everything was normal except the pressure in the cooling system and I think steam out the tailpipe at the end.

Coolant tank is maybe even a bit overfull and i hear and see it surging back in after shut down. Seems like air escaping perhaps. Perhaps I had a vapour lock but I am pretty sure there is too much pressure in there too.

Coolant tank level can be high because of cylinder pressure:(

Open the bleed off on the thermo housing and see if it has gas/air in it

Coolant tank level can be high because of cylinder pressure:(

Open the bleed off on the thermo housing and see if it has gas/air in it

Soory just seen you tried that:o: What about pressuring the coolant tank overnight if you loose pressure pull the glow plugs to see if you are leaking back?

Still looots of pressure after it sat all night. Looks like I've got a lot of work ahead of me again. I'm so glad I never became a mechanic.

i have 2006 LLY 2500hd. How much does this cost to fix in canada?

Just did them on my 2006 LLY/LBZ last weekend, They are a real PITA.

8:30 to 5:30pm Saturday for teardown then 6:00am to 7:30pm sunday for putting it back together and i still have probably another hour of things left to do to finish it up.