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strange. usually by running the heat it will cool down a motor. could be air in the system. was the thermostat changed when the radiator was done ?
hello, I would start by saying the fan comes on when the a/c is on because the a/c switch turns it on so that the car does not overheat. Do you see the fan turn on when it starts to overheat with the a/c switched off? If fan is not working then it could be your temp. sending unit or the wires from sending unit to fan. If you end up replacing the sending unit, let the car cool down then prep new one to be ready to install because when you remove the old one coolant will start to come out and you can replace new one right away so not to lose much. Don’t forget to replace any lost coolant.
I agree with bigc, this car might have a bypass valve for the heater core.
The heater core might have air in it and when you turn on the heat it lets the air through and into the rest of the cooling system.
Let me look into the bypass valve thing and I’ll get back to you.Ok, It doesn’t look like it has a bypass valve.
I would see if the heater core is blocked, A new one is like $32 bucks at autozone for your car.I still don’t see how turning on the heat can cause the engine to over heat.
Few more ideas…
You said the radiator was damaged necessitating replacement. was the car driven with said bad radiator ? if so it could have overheated causing a head gasket failure. check for coolant in the oil , on the plugs etc. prior to the radiator replacement did the car behave in the same manner ? you said the water pump was recently replaced. I would verify that it is still functioning properly. also still wondering about the t/stat . you said the car didn’t overheat with the a/c on, was wondering if this was just at idle or did it run cool while being driven ? lot’s of questions I know , just hoping we can solve this mysteryok, t-stat wasn’t replaced with radiator.. no didnt have symptoms before rad replacement. ran up to 260f and shutdown. no water contamination in oil or plugs. upper hose is hot , lower hose is cold.. found out today was a used radiator. so thinkin might be plugged. and its not my car, guy i work withs car.. a/c doesnt work.. fan works as expected. also was told has a new temp sender. ” pontiac they build excitement and a pain in the ass to work on!” hehe
Ok… providing this setup has the traditional radiator cap on the radiator try running the car to op temp , with cap off you should be able to look in the radiator neck and see the coolant flow providing the t/stat is open and the water pump is functioning. no flow and t/stat and pump are good then I would guess a plugged up radiator.Let me know what you find out.
ok this car has a surge tank a.k.a. overflow reservoir.. no cap on radiator.. cap is on tank.. some darn engineers idea..
You said lower hose feels cool. I will assume it feels like it has fluid in it. pinch off that hose ( if you don’t have the exact tool 2 pieces of wood and a c-clamp will do ) disconnect that hose from the radiator and see what the flow is like from coming out of the radiator
Hi PartsDude,
From your description, after the radiator was changed, when you command the vehicle to “heat” the cabin, and vehicle will start to overheat. Conversely, if you ask the car to “cool” the cabin, the vehicle does not overheat. What was the reason(s) for changing the radiator to begin with please?When the heat is turned on in the cabin, does hot air actually come out of the vents?
I would check the hoses going into/coming out of the heater core. Some vehicles have a bypass valve that prevents coolant from being directed to the heater core, unless “heat” is being asked for my the driver. Then either a vacuum or an electrical/mechanical switch opens up the passage way for hot coolant to enter the heater core. The heater core could be severely plugged, or be filled with air. Check to make sure both the inlet and outlet hoses of the heater core are hot once the vehicle has warmed up and heat is being commanded inside the cabin.
As 619DioFan says, strange indeed! Keep us posted.
Determine if the engine is cooling properly first. Once the vehicle is working properly (good coolant flow, thermostat working, not overheating), then look into the initial symptoms described (with car overheating with the heat on). My guess is that the real concern is somewhere in the coolant system itself. Definitely look further into the used radiator for problems. Keep us posted.
you say does not overheat when a/c is on so I don’t think there is anything wrong with cooling system, when a/c on pcm will start cooling fan so no overheating. A/C off you overheat. sounds to me like your fan does not come on. Tell me if fan is on when it gets hot with a/c off. need to check wiring to temperature sending this sending unit will ground the fan when coolant get hot enough to start the fan. I believe you may have two wires coming out of the temp. sending unit, you can ground it with key on engine off (KOEO) and it should start fan if not sounds like the sending unit . if it is I explained how to change it to minimize fluid loss, good luck.
when you put water in did you open the bleeder screw, I think you have one might be near thermostat. I apologize if I miss understood you when I read it the first time, I thought you meant turn to heat then turn to cool meaning A/C is now turned on. Check for the bleeder there may be air in there.
Bleeder screws are just there to help you fill the system faster, if you want to bleed the system follow the steps in this video. Since you have an expansion tank instead of a ‘regular cap on the radiator’ you can use the expansion tank like I use the funnel in this video so you won’t need to track down one of those funnels. To me it sounds like you have some air in the system.
http://www.youtube.com/watch?v=zUpXgAJ1gjU
Good luck.
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