01 Sunfire runs cold on Freeway NEED Your skills

[nmsunfirepontiac]

Quick summary of events:
2 Years ago car over heats and get new thermostat installed. (Road trip so had to pay a shop)

From that point on Car will run cold on the freeways in winter. Car heats up normally and city driving is normal. Summer no over heating issues. In winter car will be running 185 degrees and with in a minute of 75mph freeway driving coolant is down to 150 or lower (depending on outside temps). Heater gets hot and cold in association to the temp on dash, which conrfirms not sensor issue.

So one would think thermostat is stuck open or bad. Well I just installed another one and same issue. I also replaced the coolant temp sensor being both cheap parts and easy to get too. But when I pulled the one out, it closed and opened as should when I put in boiling water.

Problem is still same problem car is ice cold on freeway. Does anyone know if the car has anything like a restrictor plate? Maybe the first shop that fixed it remove it? The hose going to the termostat has two wires inside to insure its an idiot proof install. I have looked at Napa's diagraph of coolant system and I do not see anything other than the termostat to control flow. Everything is saying termostat but the one pulled out worked and second one does samething.

Mechanics keep telling me thermostat, but at this point I have one professionaly installed and installed the second myself and no results. IDEAS??

 

[Hewgull]

Have you tried putting on a radiator cap? Could be the cooling system isn't pressurized. Oh and this might sound stupid, but make sure the system is full of coolant.

 

[melsg5]

are the radiator fans running all the time?

 

[nmsunfirepontiac]

Cap on tight and coolant full. Car will puke antifreeze if cap is not on tight.. I know from experience....

Car has easy air bleeder on metal line going to heater to burp system so no air pockets.

Cooling fan does not come on until i think about 210. I have scanguage so can keep track of temps etc.

I actually just put a another thermostat in with new gasket; this time 195, which is 15 degrees above factory. I have improvement now car runs about 200 for low speeds but will dip to 160 in 0 degree air temps on freeway. Beats 100 it was going down too.

May just come down to doing summer/winter swap of thermostats. Still weird car worked perfect before having the shop do it....

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[planenut_2000]

That engine should have a 195-200 degree tstat only. If your watching coolant temps while driving, you will see a rise and fall in temps. thats normal operation.

 

[MaXXiS]

how long did you bleed it for? my rec is to run the car undo the coolant reservoir cap and the rad drain plug let it drain into an empty container and re use the coolant to fill up when it gets low in the reservoir do this bout 3-5 times and check your heat if everything is okay your hand should be burning after 60 sec of holding up to the vents. and yah check your rad cap. just in case, i recommend dex cool extended life antifreeze mixed 50/50. =D but gime a couple to think about it i cant exactly come up with much. atm

 

[duker_255]

Same Problem

I have the exact same problem with my 99 Sunfire. I'll be looking for updates on your success with hopes to fix mine. My next check is to check if there is something wrong between the engine fan switch and the sensor that tells it to come on. It might be running all the time and the -20 C temps just cool it of too much on the highway. Keep us posted.