Temperature gauge 260 degrees into red zone no significant coolant loss

Tiny
GARBEAR44017
  • MEMBER
  • 1995 OLDSMOBILE CUTLASS
  • 3.1L
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 150,000 MILES
The sub model of this car is SL. As I approach or at around my first mile of driving, the temp gauge needle moves into the 260 degrees red hot zone. I stop car and put in park and turn off engine. I immediately restart engine and needle moves down toward halfway mark at 200 degrees or even slightly below. Then I drive another half mile and the needle moves back toward and into the red hot 260 degrees zone. I again stop car, turn off engine, then restart and the needle moves back toward and to the 200 degrees half way mark on the gauge. This cycle keeps repeating. Importantly, I have my heater at hottest setting, and blowing full blast the entire time the engine is running. I keep left hand on the wheel and right hand over the vent, and I can note and predict the temperature gauge needle movements by the temperature of air blowing on my right hand. (I have always had a good working heater in the past). As the air hitting my right hand turns from hot to relatively cool (I do not have air conditioning), the needle moves up higher and goes into the red zone 260 degrees and the red hot light comes on. I am immediately pulling over in ten or twenty yards to turn off the engine. On some occasions here, before I pull over, the air blowing on my right hand goes from relatively cool to, what it should be, hot and the needle moves back down toward and to the 200 degrees middle mark. I do not see any antifreeze/coolant leak under the hood. Hoses appear intact. There is no antifreeze/coolant dripping from anywhere. There is still antifreeze/coolant in the coolant recovery tank. I have a theory. These described occurrences seem consistent with a pattern where there are some loose, solid or gelatinous gooey pieces of gunk in the antifreeze/coolant liquid that hits "bottlenecks" in the flow system and intermittently, temporarily stops flow, and then this stuff becomes dislodged and flow resumes. Please help. I read that my car has an 11.6 quarts (just under three gallons) coolant in the system including recovery tank. Should I flush out the system, maybe run some garden hose water flow through the system for a while ten or twenty minutes) to flush the system out?
Note: important thermostat and water pump just replaced and fan coming on and recently was replaced, radiator recently replaced
Because of this problem, my mechanic put in a new thermostat and new water pump on 12/24/16. Car was fine for a week now this problem with needle going into the red zone has recurred, and this problem is the same thing that was happening on 12/23/16, pre new thermostat, new water pump placement. Also, in September 2016, my mechanic put in a new radiator (old original radiator was leaking) and put in a new cooling fan. The cooling fans seem to be coming on okay.
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Friday, January 6th, 2017 AT 2:27 PM

4 Replies

Tiny
CARADIODOC
  • EXPERT
Thank you for including so much detail. My first thought was for the thermostat, and it still might be something to consider. I had a similar problem with my 1988 Grand Caravan, but it started to act up five years after I replaced the thermostat. The problem was caused by the heat being developed "over here" in the engine, which is where the temperature sensor for the dash gauge sits, while the thermostat is "over there", somewhat removed from where the high temperature is showing up. By the time the heat has migrated over to the thermostat and causing it to open, the dash gauge is already showing the "hot" condition. In my case, the thermostat would finally open, then the coolant would start to circulate and the cold coolant in the radiator came rushing into the engine. That caused the gauge to drop to "cold", then it started to rise again. The temperature stabilized after doing that four or five times.

The fix for this was to remove the thermostat and drill a 1/16" bleed hole in it. Many import thermostats already have that hole in them. That lets coolant circulate very slowly from where the heat is generated to the thermostat, so it will open at the right time. Why this happened to mine after five years, I do not know, but your symptoms suggest this could be a solution.

Also, consider that a leaking cylinder head gasket can do this too. That can allow combustion gases to get into the cooling system where it can pool under the thermostat. Thermostats open in response to hot liquid. Hot air will not do it.

Since the temperature drops so quickly when you stop the engine, I would look for that bleed hole in the thermostat first. The next step is to have your mechanic perform a chemical test at the coolant reservoir for a leaking head gasket. That involves drawing air from the reservoir, while the engine is running, through a glass cylinder with two chambers partially-filled with a special dark blue liquid. If combustion gases are present, the liquid will turn bright yellow.
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Friday, January 6th, 2017 AT 3:59 PM
Tiny
STEVE W.
  • EXPERT
The description sounds like a bad thermostat (yes they can be bad right out of the box these days as nobody seems to test them any longer) or you have a head gasket that is failing and heating up the water fast. Also, double check the belt routing. It is possible it was put on the outside of the water pump and is rotating the pump the wrong way. That will cause this type of behavior as well.
Could it be something floating in the system, very outside chance as it would have to stay in one spot to block the system consistently and then fall open.

Here is a quick test. With a cold engine. Start the car, let it run about thirty to forty five seconds. Shut it off and open the radiator cap. Do you hear a hiss like pressure escaping?
If yes have the mechanic run a combustion gas test and see if that shows anything.
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Friday, January 6th, 2017 AT 4:45 PM
Tiny
GARBEAR44017
  • MEMBER
Thank you for the help. There is one more thing. My mechanic told me and I did, check the dipstick oil. The oil looks "normal" in that there is no foaminess or frothiness and no smell of coolant/antifreeze which would indicate antifreeze/coolant getting into the oil.
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Friday, January 6th, 2017 AT 8:37 PM
Tiny
KEN
  • ADMIN
That is a good sign, try changing the thermostat so we can see what happens. Also lets try a head gasket test as well.

https://www.2carpros.com/articles/head-gasket-blown-test

Please run this test and get back to us so we can continue helping you.

Best, Ken
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Tuesday, January 10th, 2017 AT 11:34 AM

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