Having problems with your 1989 Chevrolet C1500 ?

Hello, I have a 1989 chevy 3/4 ton pu with a 350 motor. It reads 230-250 on the heat gauge. I had replaced both heat sencors on the side and the top of the block. Has a 180 theromstat fail safe. When it reads a high temp I pull over and feel radiator cap-it does not seem to be very hot. It doescool down eventually going down hills. Can you give some advise please.

Posted / edited by AnonymousUser on : 24-01-2022

Answers :


Physically look in the radiator under the cap for coolant level, and check the valve in the cap for sticking. If air is present in the radiator it can't get out, and more coolant can't get in,(from the overflow). Either clean the cap or replace it and check that it is the CORRECT cap.
Radiator fins dirty, clean with a strong stream of water, not high pressure water.
Radiator clogged, have it boiled out, or replace.
Thermostat stuck open or shut, replace it.
Water pump worn out, can no longer move enough coolant, replace it.
Fan shroud broken or missing....
Electric Fan(s) not working, Check the fan, relay, fuse and engine temperature sensor's.
Belt driven fan, belt slipping, fan clutch is bad, fan blades have flattened out.
Air dam under front bumper is gone, loose, or broken. It actually has a purpose other than scraping on the driveway or curbs. It forces air up into and thru the condenser and radiator. If it's loose, airflow can actually push it out of place making it useless or blocking the airflow. Along with that, there may also be a plastic piece attached to the bottom of, and wraps up behind the bumper. If it's loose, airflow can actually push it out of place blocking the airflow. Simply reattach it with 4 or 5 screws.
Also, if the vehicle has A/C and electric fans, one fan is dedicated to the A/C and should come on almost the instant the A/C is turned on. The engine fan will run even with the key off, that is normal. The system is trying to cool itself. Hope this helps.



Check all main power electrical connections first....
Electric Fan(s) not working, Checking the fan(s), relay, fuse and engine temperature sensor's.
Verify that the fans work by unplugging them and run jumper wires to the fan(s) from the battery. If they run, your problem lies elsewhere. If either does not run, it's the motor.
Next thing to check is for power at the fan connectors. You have to be cautious doing this because the engine needs to be running and warm if not almost hot, and the A/C also needs to be on. (Both must be on and running for the duration of this checklist.) The A/C fan is on the passenger side and should come on almost the instant the A/C is turned on. It is also the secondary engine cooling fan and should cycle on and off in relation to engine temperature. Use a test light to probe the two wires on each fan. If you find power the fan motor(s) is/are probably bad. If there is no power to fans, roll up your sleeves!

The temperature switch is usually located above the oil filter. If the dash gage is working, its probably OK. Next is the Fan Control Temperature Sensor, located IN or CLOSE to the thermostat housing. You will find out if it is working later is this checklist. I just wanted you to know where it is. Next is the relays and fuse's. Usually located in the engine compartment on the passenger side power distribution box. You will need to remove anything over the cover to open it. If the fuses are OK, tap on the relays or pull them out and push back in. If the fans are still not running, pull a relay and probe the socket terminals for power. Two or three of the terminals should have power, usually criss-cross from each other. Two are hot battery power, and the third is the "signal" voltage which triggers the relay to send 12V battery power to the fan. This signal voltage comes from the sensor at the thermostat. If only two terminal

You describe a system that's not full(all the way to the top and the overflow tank is full too) Or the therostate is sticking( yeah I know it's supposed to be a fail safe) or the raditor is mostly or completely stopped up. You can touch the raditor on the backside and it should be just as hot allover if it's only hot near the top it's stopped up. Or you can have a compression leak to the coolant, ( headgasket failure a cracked head, intake manifold gasket failure) with the cap off and the raditor full and the engine running ( brimming full you should nor see any bubbles. If you do the source of the bubbles needs to be found. Racing the engine (rev up) the bubbles sould not be there anytime in a good engine, The water pump could be leaking and sucking air both. air bubbles do'nt cool anything. Head gaskets and cracked parts let hor compression gfases into the coolant and it's double bad ( hot bubbles). Air in the system( not full) makes everythng rust. ( dirt does'nt flow heat very well). the part of the raditor that the air goes though can be dirty too ( spray with cleaner soap and wash out with lots of water.). The fan ( if it's hot should blow strongly and if hot you can grab it with a ragcovered hand ( or gloved) and start the engine and the fan should pull strong enough you'll have to let go If it's easy the hold back you need anew fan clutch ( freewheel cold, engage ,even lock when hot). Cheap fan clutchs blow hard all the time and are noisly and therefore use alot of gas. The good (expensive) fan clutches only engage with the water pump hot and just enough to keep things cool and only can be heard when it's real hot ( your real hot). If the raditor cap is'nt as hot or hotter than anything else the therostate or the engine not full is the problem. remove the therostate and put an asprin ( pain reliver pill) in the stat to hold it open ( for a little while) and reinstall it fill the system completly up ( with coolant mix, not water). If you may ( or even someone else) has added different kinds or antifrezze you will find that some don't mix and become a goo that does'nt flow though very well and is diffacult to even blow out with compressed air. You did'nt mention if the heater worked and if it gets real hot or not if cold it's stopped up or the system is'nt full ( back to the stst not opening) just cause it's new does'nt make it good. OE builders never use failsafe therostates and the parts stores don't reconmend them either and I never use then as they stick shut more often then not.
Repair Help & Product Troubleshooting for 1989 Chevrolet C1500

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