i just put a new t stat in my 390 and when i start it up and the motor warms up it starts pushing water out of the overflow but isnt boiling hot water. i always thought that will the loss of water when you take off the t stat housing that when the engine got warm and t stat opened that the water lvl in the radiator would go down but with mine it is the oposite. plus when it starts warming up and the temp gauge gets to right at 200 it starts jumping around like back 160 and up to 200 again still puming water out of the radiator.

no clue what is going on please help.

 

Sounds like maybe you have a air pocket somewhere. As it heats up it expands and pushes the water out. This then makes the temp go up. If and when it moves around it then cools off a bit.

Is the heater valve open to allow full flow thru it till it levels off?

 

sorry didnt specitfy i dont have the heater hooked up. out intake into water pump.

how would i go about geting rid of this air pocket?
thanks for the help.

 

It sounds like the pressure cap on the radiator is bad. Go get a new one, I use 13lb.

 

thanks that is a good possibility the one that i have is pretty old probably the original.

i will go and pick one up after work.
thanks and if that dont work then i will find some way to get rid of the air bubble.

 

Very important:

If you don't have an expansion tank and have a radiator with the tanks at top and bottom, guess what?

The top tank is the expansion tank. You should fill the radiator so that the coolant just covers the tops of the tubes, leaving a few inches of air space at the top of the radiator.

The coolant expands and has no place to go, so no matter what pressure cap you have, it will push out because the pressure will go through the roof!

art k.

 

Two things I like to do with new t-stats is to test them in hot water and to drill a small air bleed hole in them. The bleed hole helps the air escape from the backside when it's closed and helps regulate the opening rate instead of open, close, open, close. Sorry I don't have a pic of one drilled, it's about a 1/8" hole near the rim of the valve. The t-stat is installed with the hole at the top.

Searching the web, these guys talk about the bleed hole, I think the jiggle pin is to keep the hole from clogging, I never had a problem with that:

http://www.vtr.org/maintain/stag-cooling.html

(hey, i once owned a Stag)

 

If you are bypassing the heater permamently plug the holes on both the pump and intake. right now all you are doing is pumping cool water past the engine and right back to the radiator. By plugginhg the holes you are flowing 100% of the cool water through the engine. I went so far as too block the bypass from the pump to the intake also. It doesn't get very cold here. So I don't need it.

 

That's odd, I thought the pressure just went up to the rating of the cap, then the excess is blown out the vent tube, making those gooey dark spots on the highway after every pothole! Then when it cools down, it sucks air back in, until it equalizes so none is blown out.

 

Are you sure the t-stat is opening? You can tell when it opens as the top rad. hose gets really hot really fast.

Also, make sure you are not filling up the radiator "full" to the top. As krewat mentioned, the fluid level needs to be down from the top at least 1"-2". This will allow for the hot fluid to expand.

Good luck with it...and please post the fix.

 

Krewat is right... The normal level for coolant is in fact about 1 to 1 1/2 inches below the top of the radiator if you don't have an overflow tank. Most Ford trucks with an FE engine did not have overflow tanks.

 

Actually, a 1/16 bleed hole is plenty, and won't throw the thermostat off as much.

The other way to go is an airless system. That's what I do now, and I love it. The kits are inexpensive and no embarrassing overflow. It's also easy to eyeball the coolant level.

Biggest mistake people make with the airless - the cap goes on only halfway.

 

Thanks scroob, I thought 1/8 was big, looked at one of my old ones and it's around 1/16.

 

i do know that the t stat is opening becaus the top hose does get hot.

so with the heater bypassed, and the hose from pump to intake how does this bypass the motor because it is cant get water from the rad it the t stat isnt open so it is basicly? just circulating the water in the block through to the intake and back again i thought. then when the t stat opens it replaces the hot water with cool water out of the radiator via bottom hose and hot water goes into the rad via top hose explaining the increase in temp when t stat opens.
THIS IS MY ASSUMPTION OF HOW THE COOLING SYSTEM WORKS IF I AM WRONG PLEASE CORRECT ME BECAUSE I DONT BELONG UNDER THE HOOD IF I CANT KEEP THE OLD DOG COOL.

still have the problem with water running out i know that it isnt the lvl of water in the rad because after i did it for the first time i though that i had indeed over filled her and so after she got through spillin her gut i let it cool down and tried it again not adding any water same thing happend MABEY SHE LIKES GATORADE INSTEAD OF WATER .

mabey it is an air pocket in in the intake and it epands when it gets hot and pushes the water out. i will post fix when and if i can get the darn thing to fix thank you all for the help i am sure with all the suggestions that i have gotten one will be the sure fix.

thanks again.

 

Sorry we haven't hit it yet, maybe we're looking in the wrong place. What about the rad, could it be a little plugged or restrictive and can't take the surge?