2000 4.2L blown head gasket
 

My F-150 apparently has a blown head gasket. There are no signs of issues unless you drive on the interstate at 65-70 mph. The truck has new water pump, thermostat, radiator cap, and radiator when I replaced the original engine with this one from a salvage yard. As luck would have it, the problem existed when i got the engine but did not really show it self until now (after the 60 day warranty). Anyway, the heat gets hot and the upper hose will eventually get warm, but the lower hose never gets warm so there is a circulation problem. Information for a friend says that the system might be getting pressure from the head gasket leak into the coolant system that actually causes the system to "by pass" the radiator. Is this possible? If so, I wanted to remove the thermostat to allow it to circulate better while I use a liquid repair product. I know the gasket needs replacement, but I need to wait a while.

Open radiator cap when is engine cold. If coolant go out, you have pressure in system. But always is broken head no gasket in question. Why you guys always assume gasket?:-huh

It doesn't make sense to me. Let's see how water pump works.

Water pump generates pressure. It forces coolant to flow through the engine, thermostat, upper hose, radiator, lower hose, and back to water pump.

In your case, lower hose never gets warm though upper hose gets hot. Apparently, water is not flowing. You can eliminate water pump since it's new. This leaves only one possibility, a major leak in the engine. I mean a big hole. You gotta be losing lots of water. Are you?

How long did you let the engine run to open the thermostat?

I suggest you to do pressure testing of the cooling system.

As the above poster said, why do you suspect blown head gasket? Diagnosis of head gasket failure needs a little more than touching the upper and lower hoses, as far as I know.

If the bottom hose is not getting hot ,then you have a circulation problem.
Air in the coolant system can case this.
Remove the radiator cap and let it run for 15 or 20 minutes. That should get all the air out.

Why did I suspect a head gasket? A couple of reasons, the truck was getting hot then just as quickly when I turned off the engine, it would cool down. I was concerned about a circulation problem so I took the truck to a radiator shop who told me that there was exhaust gases in the coolant "which means head gasket" according to the tech. I have not noticed a water lost problem at all. No smoke if it was burning it, no water in the oil either. No loss of power.

As a follow-up, I did remove the thermostat yesterday and drove the truck for two hours or more. The temperature remained at a level I thought was appropriate for an engine with no thermostat,and coolant seemed to be circulating normally. The radiator and all hoses got warm as expected as well.

So, coolant circulation seems to be there. Additionally, I hand tested the pressure needed to open the thermostat and it appears to function normally.

Thanks for the response.

Ken

sound like the thermostat was in backwards

Agree that there was a circulation problem. Disagree that thermostat was in backward. Air in the system was what I first expected and tried what you suggested.

Well folks, it would seem that the circulation problem is taken care of for now. Seems to be running normally and I have had no issues since removing the thermostat. Thank you all for the assistance. My next step is to install a new thermostat and see what happens though I might wait until Fall.

The next question is whether or not there is still exhaust gas in the coolant after the sealant has had an opportunity to work. Although I admit that I'm not 100 percent convinced that a blown head gasket was the problem.

Thanks again!

I will try to say one more time and I would like if someone can prove I'm wrong. In 9 out of 10 cases it is CYLINDER HEAD CRACKED, it is not problem in cylinder head GASKET. I with my friends replaced in last 10 years like 20 heads or gaskets, only 2 cases was gasket. If you don't se crack in gasket it is head.

Oh, okay now I see. If exhaust gas is in the coolant, that's it. You may want to verify it yourself. If your cooling setup is like mine, there is no radiator cap. Just the recovery tank with a pressurized cap. When you start the engine with the cap off, do you see bubbles?

Whether gas is leaking through a crack or gasket, the head needs to come out anyhow. No difference at this point in my opinion.