Head gasket/cracked heads?

[77 K20]

Well, it took a month and a half but finally got my truck back today. I missed driving it. Everything seems to be fine now. With the "new to me" heads on it no longer smokes at startup.

The old heads had a cracked intake valve and the head gasket leak was on the driver's side. He said the block did look pretty good- so hopefully it will last.

 

[bucket]

 

[77 K20]

Figured I'd give an update on this. My last post was october 19th. The next week work sent me out of state- and I just got back a few weeks ago.
Started driving the truck again and on the first long trip out (150 miles round trip) noticed the oil pressure was dipping down to 15 psi from 45 psi. Pulled over and checked the oil. There wasn't any. Had to add over 2 quarts of oil. I added 1 quart of 20w-50 weight oil, and the rest 10w40. Checked the radiator: 1/2 way empty.

Made sure everything was full and took it on 2 trips into the forest service this week. 223 miles. Down 1.4 quarts, and the radiator is about 3" low. It looks like I lost some if not all the coolant out of the coolant recovery tank. Evidence of coolant on the inner wheel well and on the leaf spring on the truck. The coolant recovery tank has the coolant at the cold level when I checked it.

While driving it at night I'd get on it, then back off if there was headlights behind me. No visible smoke. No smoke at start up. Idled it when hot in the driveway at 2500 RPM, then backed off the gas. No smoke. Reved it up to 4200 off and on, no smoke.

So I don't understand. Truck starts, runs, and idles great. I don't have much time to screw around with it right now- I'm trying to enjoy what remains of the summer with the family since I was gone so long. I'm guessing maybe the block is actually cracked somewhere?

Probably start with a compression test and see what the plugs look like and what the readings are. Guess I should have just bought a brand new engine... but back when I had this work done last year I was on reduced hours and wasn't sure my job was going to last. I did what I thought would get me by for a few years and choose poorly I guess.

 

[Thunder]

I would have two questions here. Are you sure the water pump is pumping as strong as it should be? And when was the last time you had the radiator rodded? Both of these will cause poor circulation. Are you sure that your temp sensor and or your gauge are correct.

 

[77 K20]

I can run it at idle and watch the coolant swirling around in the radiator. There are no bubbles. Radiator is only about 5 years old, and looks great inside. Have only used antifreeze and distilled water in it.

I've used an IR thermometer to measure radiator temps and they match my new thermostat. The whole time I've been driving the truck lately the temp gauge says 1/4 temp, which has always been normal for it.

There is no indications at all that something is wrong while I'm driving it. It is just oil and coolant is disappearing.

I've heard it is possible to have a crack in the block that opens up sometimes during a longer drive and then will close up again at idle.... but seems very rare.

 

[Thunder]

Try running some dye through the cooling system. If there is a crack in the block it will show.

 

[MadOgre]

White smoke (water vapor) from the tail pipe?


For me that is the sure sign of a coolant to combustion space head gasket leak. If I don't see water (or vapor) issuing from the exhaust I don't immediately assume head gasket leak.

Pull the thermostat and see what happens. A sticking or failed t-stat will cause the same problems you describe. With the coolant flow from the heads to the radiator blocked off, pressurized steam pockets form. Eventually the pressure of these pockets overcome the water pump head pressure. When that happens, coolant is forced backwards through the pump and into the outlet tank of the radiator. The excess pressure in the radiator pops the cap and coolant gushes into the head tank/reservoir.

From there, it's a short trip to the pavement.

No coolant in the lube oil is another hopeful sign.

You know with all the grief associated with a failed thermostat I would think that the extra $5 for a moto rad fail safe thermostat would be justified.

I cooked a motor by starting it in the winter and then going back in side to let it warm up. COOKED IT ! because of a stupid $5.

I use the fail safe thermostats only now. Now I pull them out because my engine wont warm up because the thermostat is stuck open, not because it over heated because it stuck closed.