I just changed the water pump and thermostat on my 99 GMC Jimmy. My Radiator appears to be full and the reservoir is at a good level. The thermometer on the dashboard will indicate I am overheatign after about 10 minutes of run time (give or take a few minutes). I have checked my hoses and connections for leaks and have found nothing. Also do not see any evidence of antifreeze in the oil. A few people have told me I need to burp the system. Could it be something else? What would be the best way to burp the cooling system and if it is something else, how would I check it? I do not have a reliable mechanic to go to and I am low on cash so I will do all the labor myself.
Engine overheating and no warm air being blown on 1999 GMC Jimmy
by nsuarez91 in Bayonne, NJ on January 13, 2013
ANSWER by gmc4me on January 13, 2013
I agree with what you've been told. It sounds like you have air in the system that needs to be released. Because there is air in the system the thermostat will not open due to the coolant not directly contacting the thermostat. To get the air out you can buy a Cooling System Air Evac and Refill Kit. This tool puts a vacuum on the cooling system and when it's done you close one valve and open another that goes to a jug of coolant and sucks the coolant into the system. You also need an air compressor to use this tool. Or you can remove the upper radiator hose and fill it there then put it back on and run the engine. Check if it now runs hot. If it does still overheat shut off the truck and let it cool down. Restart the truck and as it warms up a little above where you usually see the gauge remove the hose clamp on the engine side and stick a screwdriver under the hose between it and the thermostat and wait for a solid stream of coolant to come out. Remove screwdriver and put hose clamp back on. Wait and see if vehicle still overheats. Be careful not to get burned and do not take the hose all the way off.
ANSWER by goodguy on January 13, 2013
I would run the vehicle with the rad cap off until it starts to overheat then shut it off and check coolant level when engine cools down