Rebuilt 302 blowing water after running 5 minutes

[brewchief]

I wouldn't believe the odds of buying two bad thermostats in a row. My bet is they were both in backwards.

Someone either on here or on Pirate had 4-5 bad ones in a row, wouldn't even open in a pan of boiling water.

FWIW I wouldn't fire a fresh motor up with antifreeze in the system or a t-stat, easy enough to drain down and add later after you know it's leak free and the cam break in is over.

 

[DirtDonk]

That blast out the open cap sure sounds like a possible air bubble to me too. Air in the system can give you all sorts of strange symptoms, but that doesn't usually include blowing off the lower hose!

If you have your heater hoses hooked up, you might try pulling the heat knob all the way out to let water circulate in the core. I used to aim the Bronco up a steep driveway with the heater on and the radiator cap off to burp any air out of the system.

Good luck. Hope you got it licked.
By the way, a pump can pump water and still have a leaky weep hole/seal. BUT, It's probably more likely that your leak out the bottom of the pump was actually water spraying out the lower hose up onto the pump that was then dripping down and looking for all the world like a leaky pump.
Not that you couldn't have a bad new pump of course, but the hose was a known leak point and I've had a leak in the lower hose look like a bad pump before.

Paul

 

[73azbronco]

I always test my thermostats in boiling water, the wife loves me.

 

[Vragor]

While I am more than capable of putting the thermostat in backwards (pointy end out, right?) I don't think that was the problem here. Both time I had leaks were well before the engine was hot enough for the thermostat to open.

Here's what I think I should have done to avoid problems:

I should have used just plain water during first start
I shouldn't have put the thermostat in during first start
I should have left the radiator cap off for the first 30 minutes
I shouldn't have freaked out and put the radiator cap on when water gushed out of the open radiator during the 2nd try.

The gushing water was probably the system purging itself of an especially large pocket but it wasn't through.

Lucky for me, my new quadrajet carb has the engine idling very fast right now, or I'd have totally screwed up my cam break in because I wasn't paying much attention to that part of the process with the constant worry of overheating. The zinc I added to the oil should have helped as well.

I've now run the engine for over 2 hours and driven it a few miles. It's not licensed so I can't go too far yet.

 

[fabster54]

I agree with dirtdonk, and it was prob just a combo of air and a loose hose clamp or it wasnt positioned correctly by the sounds of it.. if you let it run and drove it and it didnt boil water out. prob not a headgasket.. thats good news !!!

 

[Vragor]

As a side note, I put the thermostat in boiling water and it never opened. Left it in for 10 minutes to be sure it was thoroughly heated.

 

[77BRONKOTN]

I drill a couple of small holes in the T-stat so most of the air can bleed out before you fire the motor.

 

[73azbronco]

what brand t stat just for info?

 

[blubuckaroo]

As a side note, I put the thermostat in boiling water and it never opened. Left it in for 10 minutes to be sure it was thoroughly heated.

What was the thermostat calibrated at, and what was the elevation you tested it at? If you have a 195* thermostat and tested it at 7000' elevation, it would only open a teeny bit by the time the water boiled.

 

[Vragor]

It was a 180 degree thermostat, and I am at 7000 feet.

I bought a new thermostat last night and tested it in boiling water. It opened fine.

Put the thermostat back into the truck (pointy end out). Refilled the radiator and fired it up with the radiator cap off. I got allot of stuff blowing out but it settled down eventually. I turned it off, topped off the radiator and put the cap on.

I checked it briefly this morning and it had sucked in quite a bit more coolant from my makeshift overflow tank. I'll fire it up again after work and see if all is ok.

 

[Vragor]

Ok, putting this thread to bed.

Bronco is no longer over heating at all. Top hose gets firm after running a while and the engine is hot but not explosive hot. Drove it 20 miles without any incedent.

I think it was all just my inexperience with filling a completely drained motor.

In the future I will:

Always check the thermostat in boiling water even if it's brand new.
Either leave the thermostat out during first startup, or drill holes in it to ease burping.
Leave cap off the radiator for the first few minutes and verify water flow
DON'T FREAK OUT IF WATER FOUNTAINS OUT THE OPEN CAP
Once the engine is hot, top off the radiator and let it cool and suck more fluid out of the overflow tank.

 

[forestguy]

OK, I think I am having the same issues. I am going to take the t-stat out and let it run. While I am taking it out, I am going to make sure the pointy end is out (to the fan). This is driving me crazy