Radiator Issues

[dznucks]

i put a new larger radiator in my C-10 (350, no a/c, manual, no over flow res).
when i fill the radiator all the way up and drive the truck, the radiator will spill out some of the fluid. thats understandable. however it spills out so much that when i idle (ie. at a stop light) the engine will start to run hot. when i start riving again the temp immediately drops to normal.

Can anyone explain to me what is happeneing and why?

the hoses are new and the thermostat (190) is new.

[killer71]

Are you sure your temp gauge is functioning properly? Have you tried just filling it approx. 3/4 full to see if it does it? What concentration of antifreeze/water are you using? Out of curiosity is your overflow tube attached to radiator?

[passthebuck]

My understanding is that if you have cooling issues when driving, then its a rad size issue, but if you have cooling issues at a stop, then its an flow issue (no shroud, wrong fan, airleakage around the rad, etc.). Is the coolant spilling out at a stop because its boiling or is it spilling out & causing it to boil? If its the latter, then you could have a rad cap issue too. I hope this helps.

[shifty]

I would think it was a cooling issue - not pulling enough air through the radiator.

i suppose it is also possible that your thermostat is shot, pulley for the water pump is shot, or the impeller is busted on the water pump?

[rophle1]

Shifty, if it was the stat, pulley or pump, wouldn't he have problems at speed too? All of those things mean he's not getting the right amount of water in the motor which would cause problems all of the time, not just stopped.

I would think it would have more to do with either too small of a radiator or airflow issues. I could be wrong, my wife tells me I am all the time.

Do you have a shroud on it, what kind of fan, clutch or flex?

Ronnie

[dznucks]

i think it is radiator size too. or the cap i have always questioned it. i am going to replace it tonight. i am running stock fan, clutch.

the shroud is stock but the radiator is only slightly taller and wider but its much thicker. 4 core. it doesn't always over heat. only after it has pushed enough coolant out. the question is why is it pushing it out.

the over flow tube is connected to the radiator. regardless of how full it is, it will overflow until it is too low, then i am stuck in traffic reving the engine to move coolant through. i am not sure that it is boiling so much as just pushing it out.
i read in another post about using a heavier cap (15psi) if you dont have a resevoir. ??

[rophle1]

I would think a 4 core would be plenty big enough, is it in good shape? What's the engine specs?

[76bonanza]

How low is what you think is to low? It should not be full all the way up. And 4 core is more than plenty unless you are running lots of 4x4 climbs or something.

[clay68c10]

I bet it's your cap, how low does the level go after you let it cool off when it has overheated? It should be within 4 inches of the cap when cold. I think there's marks on the tank to show the full level.

[martinkh]

replace your cap, have an overflow, and make sure the clutch on your fan is working. Overheating at stops is an airflow problem, (almost) always. You don't have the air moving thru it to cool the coolant, because your engine speed is low (fan speed low, or with a bad fan clutch, the fan could be spinning super slow with little force) and you have no mph pushing air thru. This can be aggravated by having a cap that allows bypass at too low of a pressure. The overflow will also help, as it catches what boils out, then when the coolant cools off again and contracts, it will vacuum in coolant to keep it topped off. Make sure that there are no leaks near the cap though, the rad could have pinholes that let boiling coolant out, and then draws air back in when it cools off.

[dznucks]

thanks martin. i got a new cap, going to get a clutch. i know its old and it makes sense that it cold be slipping more.

i got to looking at the radiator and i noticed that the bottom rad. hose is twice the diameter of the top. i wonder if that has anything to do with it. combined with a larger capacity than the system needs???

its was new when i put it on a year ago, but its an odd size gm radiator for a heavy duty work truck or van.

[GREASEMONKEY72]

the hose sizes from top to bottom are gona be different, and you could always 86 the clutch and run a solid fan, let us know when you get it figured out and good luck with it

[RustyParts]

Might want to check your belt pulleys. They may be worn and the belts are touching the bottom of the groove and slipping.

[dznucks]

i belive it was the radiator cap. the new cap was alittle bit longer than the old one, not even 1/8". so i suspect the cap was not sealing at all in the radiator and fluid was being pushed straight out of the over flow tube. looks like the spring is worn, its been with the truck as long as i have had it. may be original.
with no pressure to containt the proper fluid level it was over flowing too much fluid causing it to overheat when idling.

thanks for the help guys.

[djw32]

What are the dimensions of the radiator?