Engine temp high, then normal... PLS HELP

[cparsons]

I've search through the threads, but not seeing this exact scenario...

After 20 minutes of driving the engine temperature guage tops out at hot and the air blows warm in the cab. Two minutes later the engine temp guage drops to 50% and the air blows cool. This repeated about 8 times until I got it home and back in the garage. The change in temperature is immediate, not smooth. The feel and sound of the engine does not change when the temp guage changes.

My best guess is the thermostat opening and shutting abruptly and not smoothly as designed... though that could be way off. Could be a busted sensor?

Please help!

 

[Briank]

I would start with checking for air at the bleeders.

 

[usafdarkhorse]

i would start with checking for air at the bleeders.

+1.

 

[Larry Bastanza]

What was the ambient temp when this happened?

Sure sounds like an open thermostat to me, since the car is transfering cold water from the radiator to the engine and visa-versa.

This type of temp cycling usually will happen when the ambient temp is cold (winter) and especially if you are running the car on the highway(well with the NSX, on the back roads), which will cool the radiator water very quickly.

Since your locale is Ohio, I suspect it is cold out there.

HTH,
LarryB

 

[cparsons]

Thanks for all the responses!

Yep, it was a cold day here in Ohio. Probably somewhere 35-40 F degrees. Most of my driving was on the freeway, because I took it straight home when the fluctuations started.

I'm going to replace the thermostat after work today. With a new part and the coolant flushed and replaced, that should cover both theories! I'll post back when I have a chance to test it.

 

[cparsons]

It's fixed!! :biggrin:

I replaced the thermostat and the rubber o ring with new parts from napa. Then I topped off the coolant and bled the lines. It works like a charm.

I let the engine idle for about 10 minutes until it the temp gauge was just under half way. Then gave it some gas to cause more heat which triggered the radiator fan to come on. Test passed.

Thanks for the help, guys! :smile:

 

[SOURCE 1]

Casey, Glad to hear its handled!

 

[cparsons]

Casey, Glad to hear its handled!

Thanks! Yeah, I'm pumped. Put a whole bunch of miles on it just driving around last night. :biggrin:

 

[cparsons]

Just a follow up post to say that everything is working great! Thanks again, everyone.

For future searchers: I replaced the thermostat and bled the coolant system.