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I’ve noticed rapid coolant temperature changes while driving on the street normally around town. It will increase and decrease from the low 170 to the high 190 in a matter 1-2 minutes. This is not overheating but to me it could indicate coolant is not flowing thru the system normally. I had my dealer bleed the trapped air out of the system, so I don’t think that’s the problem. This temperature swing could be perfectly normal because of the complexity of the rear engine cooling system compared to a front engine car.
Completely normal for any modern vehicle. 190 is no where close to being something of concern. Fluid heats when their is no air moving through the radiators to cool it.
The car has coolant flow control thermostat on the engine, and if you have a Z51 there is another thermostat at the inlet to the rear radiator. There are also multiple temperature sensors, but I believe (I cannot find this stated) that the one on the DIC is displaying engine block temperature. You will see the temperature of the water in the engine block rise until the engine block thermostat starts to open (it allow some small flow even when closed). But when it opens, the colder water that is in the radiators and the coolant lines starts to flow into the the block, cooling it down a bit fairly quickly. The thermostat starts to close, and it warms up again. I have seen this more pronounced on my older cars, but its normal. When the thermostat at the rear radiator opens - if you have that - you may see another brief temperature reduction cycle.
The car has coolant flow control thermostat on the engine, and if you have a Z51 there is another thermostat at the inlet to the rear radiator. There are also multiple temperature sensors, but I believe (I cannot find this stated) that the one on the DIC is displaying engine block temperature. You will see the temperature of the water in the engine block rise until the engine block thermostat starts to open (it allow some small flow even when closed). But when it opens, the colder water that is in the radiators and the coolant lines starts to flow into the the block, cooling it down a bit fairly quickly. The thermostat starts to close, and it warms up again. I have seen this more pronounced on my older cars, but its normal. When the thermostat at the rear radiator opens - if you have that - you may see another brief temperature reduction cycle.
Good input.
The change in temp change is so rapid, so I don't know if its taking the reading from a sensor in the cylinder head like the previous generation. Maybe its reporting the coolant coming from one of the radiators and not the head/block. Temp changes too quickly. I'll have to figure out where the sensor is located.
My question is what are others seeing in the way of coolant temp changes in a short time period and not whether its OK or normal, so please stay on point.
Good input.
The change in temp change is so rapid, so I don't know if its taking the reading from a sensor in the cylinder head like the previous generation. Maybe its reporting the coolant coming from one of the radiators and not the head/block. Temp changes too quickly. I'll have to figure out where the sensor is located.
My question is what are others seeing in the way of coolant temp changes in a short time period and not whether its OK or normal, so please stay on point.
I know. That's why I mentioned I have seen it on other cars. I have not driven my C8 so much in cold weather and have not noticed it. In fact, what I notice, and what other have often reported, is that it does not warm up so much at all. Some have difficulty getting to the temperature that is "recommended" for checking the oil. Anyway, here is the temperature gauge (is that on point since you asked about it?). Its not actually in the block casting. In case that part is not easy to recognize, its on the water pump.
Last edited by Andybump; Dec 29, 2022 at 10:53 AM.
I was planned to look for the sensor location. It makes a little more sense now. It's in the water pump casting so the question is is it reading the coolant temp inflow or outflow from the engine. Must be inflow because the rapid change I am seeing. The old engines had the sensor in the cylinder head, which didn't change as much. I live in central Texas and during the summer, the day time temp is near 100°, so I never noticed the temp swings I see now when the ambient is 40° lower.
Well, check these images out, that show that the water pump inlet is where thermostat is located. The area where the temperature sensor is located is called and outlet. Seem backward? I found an article (off point I suppose) that the LT1 engine did in fact have what is called reverse flow cooling. I did not find anything about the LT2, that we have, but this info in the Service Manual for 2020 Corvette appears consistent with this design. I also attached a clip about the reverse flow cooling. To me it seem relevant to what you are observing. (I agree on wanting to hear what others are actually seeing, as I have not seen it with my car).
WATER PUMP INLET
WATER PUMP OUTLET AT ENGINE COOLANT MANIFOLD (WHICH LOOKS LIKE PART OF THE WATER PUMP CASTING)
Excellent! I guess I’m just going to have to accept the 20 degree coolant swings.
By the way, I have almost 22,000 miles on my 2020 and drove it at COTA in October 2020. The highest coolant temp I saw that day was 225, which is perfectly acceptable. I never was concerned about overheating only the large temp swings that I thought could be caused by air trapped in the system.
What is odd tho is that if you're seeing this quick swing in temps at about 60F, some others might have thought it unusual, too. So far, I don't recall anyone else saying they saw it happen. But you're seemingly correct that your car is performing well otherwise including the track temp at COTA.
Coolant temperature changes
