jcwastrel

I have a 1990 full size 1/2 ton with 106,000 miles on it. I don't drive it much but it has a tendancy to boil. Like when I stop the truck after driving it a considerable distance you can hear the thing boiling. It hasn't ever over heated but the temp gauge moves A LOT. I add coolant to it quite a lot but never see anything coming out from under it. Runs fine, no extra smoke or moisture comint out of the exhaust. It has a new transmission in it. I put a new Thermostat in it a while ago. Just this year the A/C stopped working. I was told once by a mechanic who owned one like mine that the radiators that they put in these trucks were too small. So I was thinking that a 3/4 or 1 ton may have a larger radiator that would fit in the 1/2 ton without a lot of trouble. I'm a poor boy so I wanted to get a radiator from the Salvage yard. I'll put a new thermostat and radiator cap on when I change it out, but will my idea to put a ratiator from a larger truck in mine work or not? Thanks.

tinbender59

you need to do a compression check, also plan to change the intake gaskets (they get old and shrink away from the water passages), do you have white milky looking crud on the bottom of your oil fill cap? or milky looking oil on the dipstick? one thing befor you install a new thermostat, drill 3 1/8 holes just outside of the "lip" of the thermostat. still in the brass, but not in the center portion. this will let the air be purged when filling with fluid, and ensures that the thermo' gets a good flow of water arround it. my wifes Burb had a similar issue, ended up being both a cracked head and a failed intake gasket. this was found durring the Autopsy, post mortem good luck

jcwastrel

YEESH!!! I hope it's not on it's way to Chevy Heaven just yet. I have a new transmission to use up. Thanks for the advise!

2wd-K5

best place to start is the rad cap, usually when the coolant boils over it is because the rad cap failed, try it first, it is a $5 part

therewolf

Hi jcwastrel,

Welcome to the Chevy Forums.

I agree about the radiator cap, it's an ignored part that causes a lot of trouble.

Also remember that water cools, and antifreeze doesn't transfer heat half as well as water, so, if anything the water in coolant mix should be slightly higher, like 60/40, or 70/30 water, especially in hot regions.

Racers, who tear the system down often, run almost entirely on water because it cools more efficiently.

99ChevyZ71

In case you don't understand about the radiator cap, it allows the cooling system to operate at higher than atmospheric pressure, which raises the boiling point of water.

jcwastrel

Thanks!! I replaced the radiator cap and also found that the line leading to the overflow bottle was leaking where it joined up to the radiator. I cut it back a bit and put a new clamp on it to take care of that. After about 15 minutes it is warmed up and sticks around 110 degrees when at idle. I let it run for about a half hour and it stayed about the same. That's where it had been running though. when I drive it, it fluctuates between that and 210. Maybe I don't know where it should be running. Any thoughts?

therewolf

210 is good top end temp.

More than likely the center of the gauge?

jcwastrel

OK, So I got the new radiator cap, new upper and lower radiator hoses, new thermostat, even a new serp belt. Then I took the radiator out to a shop and had them clean it all out and check it. It came back with a clean bill of health. I put it all back together and it seems to be running cooler ( of course now it's a lot colder outside ). Now the issue is fluid level. I have to add antifreeze to it everyday, directly into the radiator. There is nothing leaking out if it during the time it sits and there is nothing in the overflow bottle, at all, ever. I don't get that. Am I crazy, blind, or dumb that I can't see a fluid level line on the overflow bottle? Heater and all works just fine. Antifreeze isn't really expensive, but who wants to keep putting that in everyday? Any help will be appreciated.

DoubleO7

You installed the new stat cone up, right?

The engine should come up to around 190 even at idle.
Unless your over radiated or the clutch fan is constantly "locked up" or you have aftermarket elec. rad fans that are on all the time.

A steady 110 no matter how long it idles is nearly impossible to maintain.
And not good for the engine either.

Fil the overflow tank half way. The fluid should only vary a couple of inches in the tank between full hot and full cold.

Maybe it is leaking out only when being driven?

Did you re-connect the transmission cooler lines?