Today was the first chance to take out the truck in a year after painting the bed and getting the engine rebuilt into a 390. Break in was a bear as the temperature would always hit H. Took four 8 minute runs to finish. Use laser gauge to check temps and the hottest I would get is around 240 in the heads and 230 behind the thermostat. Upper hose at 186 and lower hose at 134.

Maybe just my dash gauge so cross my fingers and out we go. Ten minutes to get gas and the engine is at H in 5 minutes. Get on the freeway and it is on H for 4 miles before boom. Throw into neutral and start coasting across 4 lanes of a 6 lane merge of two freeways to reach a safe dirt shoulder.

Stop and the white steam pours out. Open the hood and see that the top hose at the engine end was blown right off the water neck. Quite a thing given how hard that was cranked down. Waited 1 1/2 hours to get a flatbed back home.

When home the engine took 2 gallons and I started it up fine to back into it's driveway. Now the fun begins and that is WHY? I know the gaskets are right since the square edge of a Felpro sticks out at the lower front corner. Two 180 thermostats have been used just in case. Although I know the first one worked as I left the cap of earlier and water gushed out of the radiator telling me the thermostat opened. Of course this would happen one month before we move and the truck can't travel.

 

Is the stat upside down? No other reason for the engine to overheat so quickly unless there isn't any coolant in the block. Try running the motor without a stat and take its temp. Put a candy thermometer in the radiator and compare with gauge on dash. If you look in the radiator while the engine is running and you see the water circulating, It should not overheat. If it does get hot, check for a clogged radiator.

 

A few years ago I totally rebuilt the 390 in my T-Bird and I experienced overheating problems. It never overheated before so I was baffled. I dumped a few grand into the engine using new brand name parts and a CJ cam and lifters. I didn't drive it home I had it towed home and started to investigate. I checked the timing first and that was right on. I remembered one change I did and that was to replace the original fan with an aluminum flex fan. I went back to the original fan and it still got hot. I removed the thermostat (a 190, 390's like to be warm) and tested it on a stove with hot water and a candy thermometer. It worked fine. The next thing I did was to remove the water pump and check the impeller, it was the small impeller from the re-builder. I took it back and before I left the parts store I had them remove the plate and check the impeller. it was the correct large one.

So I replaced the water pump and used the original fan and it worked like a charm. Later I switched over to the flex fan again and it worked good, no overheating problems to this day.

Back then I didn't know there were 2 sizes of impellers and the parts guys thought they were all the same also. The re-builder had poor quality control or someone stuck it in the wrong box.

Maybe you have a similar problem,
Hope that helps and good luck.

 

That was already checked and the spring is towards the engine. Tried once to run it with the cap off to watch but when the 'stat opened the water shot out the radiator opening like Old Faithful all over me. First time I have ever seen water do that rather than just smoothly running past the opening.

Next would be with no 'stat. As for the radiator I am not leaning that way as the water leaving it through the lower hose is the coolest point of the engine.

 

Sounds like you have a huge air bubble in the system. Try using a flush and fill kit that will insure there are no air bubbles in the system and make sure your heater is open.

 

Sounds like combustion gasses in the coolant, caused by a leaking head gasket or cracked head. If you start it up with the cap off, does it have a lot of bubbles or overflow?
It should not be getting that hot so quickly.

 

Of the four possiblities:

Head gasket
Thermostat
Water pump
Pressurization

I'm leaning towards pressurization as the head gaskets and stat are correct. The water pump is working based on the 1/2 foot geyser out of the radiator cap opening. So what forced the water out like that after the stat opened? Pressure behind the stat.

 

If combustion gasses/compression is entering the coolant, it will superheat it and push it out where ever it can.
There is a test kit available to check your coolant for gasses.....check with your better part stores or speed shop.

BTW, did you torque the head bolts in proper sequence to correct torque?

 

water shooting out of the radiator is from steam building up in the engine not the water pump working too good. Sometimes air gets trapped in the engine and it is difficult to get it all out.

 

Ok, not a bad night with the truck. Still have questions about the trucks original temperature gauge.

Put water into the radiator at no more than 1' about the fins and 1 3/4" below so I had room to expand. Left the cap off and put that elbow on that you get from the Prestone back flushing kit. At least that way water will go forward. Start the engine and up to 1400 rpm while watching the gauge.

Takes the gauge awhile to move off C. About 4 minutes in 1-2 pints of water comes out that elbow. Gauge still at mid way only and I pop out from the cab. Take a look into the radiator and see rushing water with no bubbles of air. Start using my thermal thermometer and get 185 in the top hose, 205 behind the stat, and 225-230 on the heads. Let the truck run for 20 minutes and the gauge just falls short of the first line by H. My gauge has two lines at each end. Kitchen thermometer in the cap is reading between 195-205 the whole time. Ran it at idle and up to 1500 rpm without any temps rising.

So maybe it was the biggest air pocket inside the engine and it had an embolism during that drive. I do know about the compression leak tester to detect exhaust gases in your coolant. May get tomorrow. May also get a VDO gauge that can read the temp in degrees to actually watch what is going on.

 

Getting all the air out is difficult at times, I've had them blow the coolant out as many as three times. On the last two engines I built, Yblocks but same principle, I hooked a short piece of 5/8 hose to the fitting on the manifold for the heater, attached a funnel and filled the heads/block with water from there. It actually filled the radiator from the bottom at the same time and required little additional to top off. After starting it showed very little air in the coolant.

 

look at your thermostat and check to make sure there is a tiny hole in it to relieve pressure and air . Some aftermarket Chinese ones do not have it which in that case you just make a 1/16" hole .

 

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There was one because I drilled the hole myself. Even the Made in USA Stant thermostats do not have a hole today. Yet that was on the first start up of the engine when it actually blew a geyser out the open radiator.
Next time either I'll leave the intake heater hose fitting off to bleed air or fill from there as suggested.