Can't figure overheating problem
 

On cool mornings my temp seems to stay good (right below center on the guage). Except when I do a few revs above 4k, then the temp shoots up to the top mark right below the "H." As long as it is cool outside the temp will gradually go back to close to normal as long as I don't drive it moderately hard. Now on a hot day (say above 90 degrees) the temp will not go back down unless I turn the heat on. When I turn the heat on it almost instantly drops close to normal, but never will it go all the way back down.

Here's what I've tried to do so far:
Changed the thermastat with a 180 degree
Flush the radiator several times
I still have the fan shroud, and fan/clutch has been replaced.
Tried removing and reinstalling all of the plastic parts (skid plates, and fan shroud).

Thanks for any help you may have.

Are you constantly having to refill your coolant?
If so.. is it leaking on the ground anywhere?

MAZDA THERMOSTAT!!!!!
MAZDA RADIATOR CAPS!!!!!
PRESSURE CHECK COOLING SYSTEM!!!!!!
ROD OUT RADIATOR!!!!!!!

How old are all the hoses?
How old is the water pump?
Check the water pump housing for erosion, which reduces flow.

I would change out all the hoses. have a rad shop rebuild radiator , install new water pump and switch to EVANS NPG+, but hey I don't have a cooling problem anymore.

Ok, I don't have any coolant leaks at all. I fixed an oil leak yesterday which is the only leak I've got. Another thing is when it does run that hot is NEVER boiled over. I've never had coolant on the ground anywhere. I've pulled over when it is that hot and shut off the engine and no coolant, not even the smell of it.

The water pump about 1 year old, I had to replace it because of a crack. It was just old. The hoses are old, I could replace them. How could I go about "rodding" out the radiator, or should someone else do it?

Take the radiator to a radiator shop and have them flow test it.

Where in SC are you I'm near aiken

If it goes all the way up to the H and you have not damaged the engine, I would say that the gauge is bad. Overheating the engine (repeatedly according to your post) would have damaged the engine by now. I'd start with an aftermarket temp. gauge. You also need to make sure that you are getting ALL the air out of the system when you refill it.

Todd

"H" on the stock guage is 250*F. At that temp, you've got a crispy engine (ruined). It basically has 3 positions :
1)cold
2)normal (174-249*F)
3)Hot (250+)

I reccomend getting the FSM from www.iluvmyrx7.com and do the procedure for checking the guage. Get an aftermarket guage to see your actual temp.

Ok, I'll admit something. I actually have an '86, and I bought a guage cluster from a '91. I had to move the wires around on the plugs to the back of the guage cluster in order for it to work. I guess from all of the guage situations above, does the '91 guage use a different resistance than the '86 guage? I've thought of taking a potentiometer (pot) and try to test it to ground. Which would seem to me to work by the way the fsm says to connect the guage to ground and it will read HOT. I'll try that. Tell you the truth, I actually bought the sensor for a '91 model to connect and it will not fit into the engine. :) Thanks again.

My info. says that the gauges are different. I would not trust that gauge....just get an aftermarket gauge to be sure.

Todd

As long as you have not boiled over, the aftermarket guage comes first.
My old 87 had two problems that caused it to run hot. What finally fixed it? Would you believe the water pump housing? The aluminum casting behind the pump was eroded by the turbulence of the high revving pump. The bypass valve seat under the thermostat had about a 4mm chamfer eroded away, and there was a 6mm hole eroded through the internal wall between the inlet and outlet side.
All this bypassing gives symptoms like a partially blocked radiator. I fabricated a repair with Bondo Marine Epoxy Putty Stick.

Alright, what I will do tonight is measure the resistance of the '86 sensor and the '91 sensor. That should eliminate any discrepencies between if the '86 guage is different than the '91. I will also look into an aftermarket temp guage, and see what temp it is coming up with when my guage states it is running hot. The amazing thing is that when I turn on the heater the guage instantly drops to the center position. Also, I can let the car idle (with the AC on) forever without running hot, it only happens when I do a couple of high revs on the engine or it is already real hot outside. Thanks everybody, and good luck on your cars as well.

Ever think of making sure that that the fan clutch is functioning properly. You mentioned that you replaced it, but was it a brand new one, or from the junkyard?

That would be my first guess over everything that others have posted. The symptoms you explained are typical of that clutch not spinning the fan fast enough to keep a sufficient amount of air flowing through the radiator.

When the engine is hot and you rev it up from idle to about 2500 and hold it there do you hear the fan roar for a while and then eventually slow down? That's what mine does and it makes me feel confident that the clutch is doing what it is supposed to do. When I first start the car cold and the RPMs go way up my fan roars for a few seconds and then slows down to normal then too.

Just a thought.....you might want to check it out. Could be something that simple.

My car has been running very hot too like half way I hav eboth stock gauge and and after market set. When I turn on the a/c it goes up to almost 240 yep that hot !!!! With out it it runs around 205. I hav eflushed it several times and drianed the block with the plug below the spark [plugs also mazda stat and caps new !! also just put in a brand new water pump tonight and Bingo the housing is all erroded away where the impellars are !!!!! It should be machined there but it is nasty as hell looks like the moon's surface its so bad . So with out one I just put the new water pump and every thing back together not much a difference at all !!!

That was also one of my thoughts 91vert. It doesn't roar like I thought it should, but I had someone look at it and they said it looked fine to them. My neighbor also has an RX-7 and it will about knock you down if you stand near the engine bay with the hood up. I'll also look into the fan clutch.

get a mazda thermostat. And as long as all the stock plastic is there, that's all I've got to suggest. Everyone else has suggested the other stuff already.

The fan has nothing to do with cooling at highway speeds, it's purpose is to keep air flowing through the radiator when the vehicle is stopped. At highway speeds, enought air should be moving through the radiator to bring the temps down. When you turn on the heat and the temps drop that indicates that not enough heat is escaping from the coolant in the radiator to keep the car running normal. With the heater on you are actually running the coolant through another radiator, the heater core, in the car and blowing air across it to remove heat from the coolant for the cabin.
I just recently went through the ordeal of hunting down an overheating issue. All of my plastic was in place along with the belt driven fan and shroud. Come to find out, my thermostat was stuck and my radiator cap was bad. With the MAZDA DEALER cap and t-stat, my temps run much cooler, about 1/4 - 3/8, city or highway. It runs up to 1/2 when I get into the turbo, but gets back down to normal, 1/4 - 3/8, in a few minutes.

Good luck and reply back with your results.

:mad:

When was anything mentioned about highway speeds???

Geez!!!

This lets us know that the fan clutch assembly is working fine.

Last Thursday, it rained VERY hard and flooded some of our roads temporarily. I accidently ran into one of those roads not knowing how deep it was. I ended up with about 3 inches of water over the top of my hood, and some came up my windshield. I was able to keep going without stalling, and miraculusly I havn't had it overheat once since then. It did go about 2 thirds up this weekend but it was over 100 degrees outside. It screwed up my altinator for a couple of days, but so far my temp seems to be working great. I'll keep an eye on it, and don't have a clue what the water could have done to help. Thanks again.

Maybe I should have driven through one of those "puddles"

It could have cleaned your radiator fins........;)