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2001 Olds Intrigue overheating?

my old lady has a 2001 olds intrigue with the 3.5L in it. Sunday evening we replaced the Throttle Position Sensor and the Coolant Temp Sensor. Monday she was on her way back to Iowa and the tempature gauge spiked up to the Hot area. I looked it over and could not find anything wrong. I sent her on her way and she made it about a mile before it did it again. The car will spike up to the hot area but the motor shows no signs of over heating. I checked the temps with a heat gun while the car is idling and read out Thermostat housing-160, Rad-80, Rad hose-130, and coolant 170. I than ran the car up so it shows on the gauge its hot and than checked again, it than reads Thermostat housing-172, Rad-100, Rad hose-134, and coolant 184. If I am running it at 1500 rpms it will spike up but once i take it up to 2500 rpms it drops back down to normal on the gauge. I am lost for what it could be. Somebody please help me out. Thank you!

was the car’s temp gauge doing this b4 you cahnged the temp sensor?its also possable tha tthere is an air bubble in the system or it could be a defective sensor

why did you change temp sensor? 3.5 is a motor cloned from the infamous caddy northstar which is known to have headgasket issues. i see quite a few 3.5 intrigues being junked for motor issues but i almost never see the intrigue with the buick 3.8 suffer the same fate. how is your coolant level?

I changed the Sensor because it was throughing a code, it was not doing it before I changed it though. I pushed air out for about 3 hours yesterday afternoon. I was told on the 3.5 it can be a pain in the ass to get all the air out. The head gaskets and heads were replaced less than a year ago. There is no white smoke, no water spitting, and no mixture in the oil. Yes these 3.5 liter motors are a pain in the butt always have been. i am a mechanic myself and this is the first time I have been stumped like this. On these do they need the OEM sensor? I just bought the cheap one from NAPA.

Oof. Did u change heads? I assume u did not since you would be very experienced with adding coolant after that job. I am not sure if 3.5 has same coolant crossover design as northstar. The NS has a purge line that allows air to escape to surge tank and can get plugged. Don’t know if 3.5 has same issues on trapped air

The heads and head gaskets were replaced a year ago!

Sounds like the cooling system is able to disspate the heat when the engine is idling, and even dissipate excesss heat, but not so when it’s revving or under load. We both know what that means. When it’s under load one of the cylinders is probably blowing hot combustion gasses into the coolant.

Time for a leakdown test. Whatever was the root cause of the headgasket failure a year ago apparently still exists.

Post back with the results. I’m curious as to the accuracy of my assumption.

I am going to change the sensor again with the old sensor and see what it does. Because like i said in previous comments it was not showing hot until i replaced the sensor. There is no signs of a head gasket leak or anything. It blows no smoke, there is no water splurting out and there is no signs of water in the oil. The motor shows no signs of over heating also when the temp gauge claims it is. I am hoping for a faulty sensor since it drops once revs reach 2k rmp

Take a close look at the connector and wiring to the temp sensor.
Maybe spray some contact cleaner in there and make sure the metal “fingers” are tight.

Before you go thru all that, try this.

Get the engine hot. While the engine is idling loosen the upper radiator hose clamp and take a small flat bladded screwdriver and slip it between the upper radiator hose and the radiator hose neck. Allow the engine to continue to idle until all the air purged out of the cooling system and nothing but coolant comes out. Remove the screwdriver and retighten the hose clamp.

If there’s air trapped in the cooling system, and this air reaches the water pump, it can cause the coolant flow to stall causing the problems you see.


okay thank you!

I know u said heads were done last year. Did u do the work? Never seen bleeding air out a loose hose clamp before. Is that a GM master mechanic trick? Does the 3.5 motor have anyway to bleed air out of the cooling system? Like a valve on thermostat housing?

I unplugged the sensor to see what it would do an the car read normal temp after about 20 mins of idling??? I am beyond stummped on this!

It has a bleed off valve on top of the radiator. I did not do the work. It was done at a place down in Kansas

@Stoveguyy that loose hose clamp procedure is not exclusive to GM. It is old school, though. But it sometimes works.

Did you turn the heat on when you bled the system? If that fluid valve on the input to the heater core isn’t opened, the coolant won’t flow into the core properly and the system won’t purge fully.

I did have the heater on yes. The thing that is stumping me the most is the gauge will read hot but the motor at no time is hot. I can grab with my bare hand and its a normal hot not a super over heating hot. And when checked with the Heat gun I get all normal readings.

It’s gotta be either the sender or the gage. Or an “open” (high resistance, perhaps hanging by one strand) in the wire that’s being affected by temperature. String a new wire and see what happens.

Do these cars have a sending unit or is it all controled by the temp sensor? I cannot seem to find a sending unit anywhere…and how would I go about doing the new wire? I checked the ohm reading on the connector wires and it was a 4.26

I’m using the word sender to mean sensor, so please bear with me. I don’t know where the coolant temp sensor is located, but perhaps the attached link will help you find the location.

Running a new wire just means disconnecting the existing wire from the sensor to the gage (or its wire on the harness) and spliciung in a new one. Typpically I’d do it with clips, just as a diagnostic, disconnect the old wire at teh sensor end only, and see what happens. If the symptom disappears, than I know the problem is in the harness and I’ll run a new wire through a permanent route and just clip the old wire and leave it unconnected at either end in the harness.