As seen in this thread. I recently installed a Stewart Warner water temperature gauge. The sender for the gauge is mounted in the top of the thermostat housing. I noticed something interesting last night while driving my car.

Under normal cruise my coolant temp stays at a consistent 180 degrees F. After cruising on the highway and paying a toll, I floored it coming out of a toll booth. The temperature DROPPED to 160 degrees briefly (~5 sec), then rose to 200 degrees after getting off the throttle (I wasn't on the throttle for more than a few seconds since I don't want to break the speed limit), after getting off the throttle and cruising normally it slowly returned to 180 degrees.

The ambient temperature was near 20 degrees F.

I feared that I still had air in the system after installation of the sender, so when I got home that night I parked the car, and this morning I checked the fluid level, it was fine.

So I tried it out again this morning, similar ambient temp (~20 degrees) and the same thing happened.

My theory...

The ambient temperature was so cold that the thermostat is only open slightly to allow enough cooling for the engine at a light throttle cruise. When I floor it, the water pump demands much more flow from the radiator at high RPMs. The volume of fluid in the radiator is much cooler than the fluid in the engine due to the cold ambient temps, causing rapid cooling of the engine and a momentary drop in coolant temps. Then when getting off the throttle the coolant flow slows, and the coolant heats up more because it is flowing slower, causing the rise in temp when getting off the throttle.

This is the only explanation I can think of. I do not believe my water pump is cavatating since I have an underdrive pulley. I also do not believe that an air pocket could cause the rapid drop in coolant temps only while flooring it. The sender is screwed into the aluminum of the t-stat housing and heat is being transfered into the sender through the metal as well.

Am I crazy? Has anyone else experienced this?

- Steve

 

ttt

 

Well, after talking to some car guys at work who also happen to be engineers, we're all in agreement that this is normal and caused by the rush of cold coolant into the engine from the radiator.

Anyone feel differently?

- Steve

 

Seems normal to me.

Stupid question, but does anyone know which is the feed and which is the return lines on radiator? I figure the top line is the feed line?

 

Water is pumped through the Engine, out the termostat, through the upper hose into the Radiator. The lower Radiator hose feeds the water pump.

 

thats why you try to put the sender in the block.. you wont have this, and you get a more accurate reading next the cylinders, where it matters most..

 

Your theory seems to make sense to me.

 

Wow, I wonder why mitsu didn't put the sender in the block then?

 

the factory gauge does not show the constant temp changes as much.. as to where an aftermarket will..

 

Wow, really? I guess that might have been the reason to get an aftermarket gauge, to get accurate readings.

 

Wow, really? For a second there, I thought we had a smart *** on our hands

 

Stock Temp senor is in the block. He was talking about your sender placed outside the block.

 

^^ Not on the block but located in the T-stat housing up in the cylinder head.

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Exactly, it's about 1.25 inches away from the sender I just installed, which is right on the other side of the t-stat. Once the t-stat is open, any fluctuations I get on the aftermarket gauge would be seen by the stock gauge too, you would think anyway...

- Steve

 

well how about this, sit and look real close at the factory gauge and you will see it move.. i have dealt many times with placement of sending units on small and b.b chevys, sensor local will make a diff.. all depends on what you monitoring, how you want to monitor. block, heads.. why the hell am i explaining myself.. screw this..