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Followup To
Question -
I have a 1990 GMC Suburban 4WD 1500 with the 350 gas engine. Recently I noticed that I was getting little heat. Checked upper and lower hoses and they were hot, so I replaced the thermostadt. Better, but not by much. After running the truck for one half hour both hoses were hot, but the radiator was cold (all over). Never have run into this before and wonder if you have an idea.
Thanks
Answer -
Air can sometimes get trapped in the cooling system.
If you can find a steep hill to park on, park you truck nose up on it overnight. Check the cooling system the next morning and you will likely find that you have to add some coolant.
If you do not have a hill, you can jack up the vehicle and support it with jack stands. Check it the next day and add coolant as required.
You often have to drive the vehicle, when it is cold outside, to get the radiator hot from coolant flowing through it.
Thanks for the reply. I tried your suggestion to no avail.
Couple things I didn't mention is that the truck has a rear heater and the hoses are hot on both sides of either heater. The temp guage only reads about 120 degrees and, if there was air in the system, wouldn't this system boil over?
AnswerI have no experience with rear heater systems, but my Toyotas are mid-engined and have heater and main coolant tubing from the rear axle to the radiator behind the front bumper.
They also have bleed valves that makes getting the air out of the cooling system very easy.
If you are running a 50/50 mix of antifreeze and water, the boiling point is about 260 degrees F with the radiator cap on and about 230 degrees F with the radiator cap loose or off. Air in the system will not cause the engine to overheat if the there is enough coolant to make the thermostat open.
Did you install the correct thermostat? Does the coolant level in the radiator overflow container rise with the engine warm and drop when it is cold? What is the outside air temperature when you idle the vehicle?
