Chevy & GMC Vans

So I'm new to this site, you guys rock! This site is very helpful. But I have a 1991 astro rwd that wants to overheat when going up hills. It drops back down after just 5 mins or so but it worries me being that I have the heater fully blasted and it stills is on the verge when climbing hills. Why would it do this?

from http://www.arrowheadradiator.com

First: Is there enough coolant/antifreeze in the radiator? Don't just look inside the plastic overflow bottle, but remove the radiator cap (when the engine is cold) and look inside the radiator. You should be able to physically see the fluid level if it is at its proper level. Most cars and trucks will hold 1 1/2-2 gallons of coolant and water mixture. If you have to add more than a pint of fluid you should have the cooling system pressure tested for a leak. If you see any obvious fluid loss on the ground or in the engine compartment, you should also have the system tested for leaks.

Second: If no coolant leak or low fluid level is present, then determine when the overheating complaint occurs.

If the engine overheats while at a stop or idle only:

....electric cooling fan motor located in front or behind the radiator. The function of the cooling fan is to improve airflow across the radiator at stops and low speeds. The fan is controlled by sensors that regulate the engine temperature and additional load that might be placed on the engine.

The air conditioning compressor will require the cooling fan to operate at idle as long as the compressor is on. A quick way to check the cooling fan operation is to turn on the air conditioner. The cooling fan should come on with the air conditioner compressor....The radiator fan is responsible for engine cooling, and the condenser fan is responsible for increasing air conditioning efficiency at idle and low speed.

If your vehicle does not have an electric cooling fan on the radiator it will have a belt driven fan blade and fan clutch. This fan should be pulling a large amount of warm to hot air across the radiator onto the engine. What you want to determine with either fan situation is that there is ample airflow across the radiator at idle. The radiator is the primary heat exchange for the engine, and airflow is crucial.

...airflow and coolant circulation are crucial. At 55 MPH we can assume you have ample airflow across the radiator, so proper antifreeze circulation is the thing to inspect. I compare overheating at 55MPH to jogging with a sock in your mouth. The faster and longer you jog, the more air you are going to require, and with a sock in your mouth you are going to have to breath extra hard to maintain the proper amount of air to keep you going. At 55MPH the water pump is pumping a large amount of hot antifreeze throughout the cooling system.

If there is a restriction in the system like a kinked radiator hose, a restricted radiator, or a stuck thermostat, it will produce the same affect as the sock in the mouth scenario. Rust and water calcification can accumulate in the radiator and drastically reduce the flow of coolant at high speeds. Removing the radiator from the vehicle for disassembly and cleaning or radiator replacement are the only two real cures for a clogged radiator.

Using a can of "radiator flush" additive might help as preventive maintenance, but will probably just be a waste of time and money trying to correct a restricted radiator. You can read my past article about radiator flushing by clicking on this link: Flushing your Radiator and Cooling System

Good tips.

The problem with climbing hills his threefold. #1 you're probably moving slowly so like samsquantch mentioned, there isn't enough airflow to take heat away and the radiator can't do its job. #2 the engine is working hard and generating lots of heat and #3 the transmission is working very hard too! Slippage in the torque converter heats up the trans fluid a lot and guess where it's cooled? That's right, in the radiator.

All that being said, I think you have a problem, because the cooling system should be able to handle hill climbing. It could be a number of things. As was mentioned, start with coolant level. If it's down you could have a leak (which you will be able to see underneath), or a faulty rad cap that lets out steam (you won't see). Since your heater works fine, I'm going to say your coolant level is probably fine.

It is true that antifreeze will elevate the boiling point of water, the point at which it turns from liquid to gas, which is important. By pressurizing the system, the rad cap also helps to keep coolant in liquid form. But antifreeze DOES NOT help keep the temperature down. In fact it does the opposite. What most people don't understand is, antifreeze is poor at carrying away heat. Water does a much better job. So you could have 90% ethylene glycol in your system circulating around and it won't boiling, but your engine temperature will be critical. You want just the right proportion to keep it from freezing.

I don't agree with pressure testing and here's why: if you don't have leak, this is a good way to create one. Use it as a last resort.

Another point of failure is the thermostat. These are ingenious mechanical devices and are usually reliable and durable. It relies on the predictable expansion of wax to open and close a valve. To recognize if it's failed, you kind of have to observe your temp gauge closely, and watch how the temp rises and then levels off. If it keeps going up, or fluctuates wildly, you could have a bad t-stat.

Once you make sure there's enough coolant there, you want to make sure it's flowing. Disconnect one heater hose and see if the water gushes out forcefully. If not, your water pump could be going out. Your van will have a belt driven cooling fan. It's it's not spinning properly, the fan clutch could be bad.

If you do a lot of steep hill climbing, you should look into a transmission cooler after you get this cooling problem figured out. It's kind of a weak point on these vans, and will help prolong the life of your transmission.

Hope that helps!

Check your thermostat it might not be opening right. Also get the van up to temp and then feel the front of the rad for cool spots you might have blocked passages in the rad thus reducing the cooling capacity of the rad.

I would change the thermostat and then look at the radiator. It is 20 years old and probably needs replacing anyways. I am sure the tubes are partially if not fully plugged.

Thank you everyone for the tips! Its highly appreciated!

The Coolant level is a bit high, pretty much an inch or two down with the radiator cap off. The van does just fine around town its just once it hits hills I lose a lot power it feels like then after about 5 or 10 minutes of climbing(I work on Mt.Hood in Oregon) it starts heating up almost to the Yellow on the gauge. After sitting for about 10 minutes or driving around as long as its not up hill, the engine starts to cool down and back to the center of the gauge. Ive had the radiator flushed when I first purchased the van in February and a new radiator cap was put on.

I was thinking of starting with an air compressor and cleaning out the radiator and replacing the hoses as well as the thermostat.

Which is the best brand of transmission cooler to get?

Thanks again!

Lets see if you have another type of problem.Start it up and let the thermostat open to operating temp leaving the rad cap off.After the thermostat is open(you can tell by touching the top hose and if it is hot then it is open).Then look into the rad.If you see a steady stream of bubbles then you have a blown head gasket or cracked head.That would pressurize the coolant system preventing from cooling correctly under a load.It's a long shot,but one that won't cost you anything but your time to check.

Derek939 wrote:Thank you everyone for the tips! Its highly appreciated!
The Coolant level is a bit high, pretty much an inch or two down with the radiator cap off.
Thanks again!

Really? I usually fill my rad right up to the top till it runs over almost, then twist on the cap.
If I saw it two inches below full, I would be looking for leaks after I top it up and get it hot again.

So, Are you talking about the level in the overflow bottle then?
If so, I wouldn't believe that so much, and I would look in the rad.

Im gonna go check for that here is just an hour or so Gary, thank you! Never hurts to check at least.

And no the radiator has always sat just below the cap and never usually leaks. There is on small leak on the top of the engine block where you put oil into the engine it has a brace that runs down and bolts into the engine. There is a tiny bit of antifreeze that leaks from there but I think its because that bolt is loose. It wont tighten and I do not want to snap it off. Im hoping this wont cost to much money to fix.

The rad shoud be filled right to the cap. If your rad is down chances are you have air trapped in the top of the engine and heater core. When you climb a hill it works the engine harder and probably burps the system and that's when you see the temp gauge go nuts. You could be running hot nearly all the time and not know if your temp sensor is in air and not coolant.

It usually gets up to the middle between what the gauge reads in the picture and the yellow line. Not yet reached yellow line though.

Sorry for not replying recently, I just had a new muffler installed so I've been preoccupied with that.

Also I took off the radiator cap and started the engine but within 1 minute the fluid
Level started raising and overflowing slowly. Is that normal?

Thanks guys!!

Just noticed my image before did not load. This is what my gauge climbs past as i start climbing hills. It has only so far come up JUST below the yellow marker. Not sure if that is normal? I just got a new T-Stat to see if its a simple fix.

Am I reading that right -- only 86K miles on your van?????

186xxx on the van! I wish it only had 86xxx!