COsborne

After driving to an autocross I noticed on the way home that the car was getting getting hot at 80 mph or so. It never overheated, it would just run about here:



So when I got home I figured it was just b/c its going into summer and Im a new rx7 owner. Thats too hot for me so I figured it might be b/c Ive removed my A/C and air pump so I put a 21 1/2 inch belt from the underdrive pulley to the waterpump:


Yes, its dirty...havent cleaned it yet

...that didnt help so I removed the fan shroud and fan and installed an electric fan. No better results. Even though the problem is only when I push the car or drive at 70+ I replaced the thermostat with a 180 degree one as a maintainance thing. No result. Replaced the radiator, no result. Replaced the sensor at the bottom of the radiator with one of my spares not sure if that would possibly give me a result but it didnt. So now the only things left to replace are the water pump and sensor by the rear trailing plug. The pump doesnt have any play in it and turns freely. Im about to go out and replace the sensor....Im not sure why it would start to fail in this way though. Any feedback would be appreciated.

COsborne

oh yeah....changed the coolant couple times too

Felix Wankel

You may want to try to find the plastic undertray that goes under the engine.

My car runs warm like yours, once I go above about 75 mph, I figure its due to my undertray being gone. Its the only thing left that I haven't gone though...

NZConvertible

Here’s what I think. The belt directly to the water pump is a good idea, but the underdrive pulley is not. The pump may not be turning fast enough. The stock fan cools amazingly well, so replacing it with an electric one won’t help; but the fan makes no difference at 80mph anyway! Was the thermostat a Mazda one? That’s important. The sensor at the bottom of the radiator is part of the emission controls, not the cooling system, so it’s not that. The sensor by the trailing plug is the temp gauge sender. It could be that, but they normally just fail totally, not lose accuracy. Since the radiator’s new, IMO the pump’s condition is the most likely suspect. If the engine was run without proper coolant for any length of time (by a previous owner) the impeller may have rotted to the point where it can’t pump fast enough. The U/D pulley will be making this worse. I think you should pull the pump off and inspect it. There’s a good how-to at www.fc3s.org.
Good luck, hope you sort it out.

NZConvertible

****, didn't see that missing undertray! Good spotting Felix. Definitely replace that. It's what forces the air through the radiator instead of under it.
Won't you be mad if that's all it was...

COsborne

since I dont have problems at idle I think the air deflector idea is probably a good point...

How well does this work:

http://www.fc3s.org/deflector.html

Felix Wankel

Ive been trying to find one of those damn undertrays on a junk car. Its harder than I thought it would be

Felix Wankel

You need the one that goes under the car as well. You're not supposed to be able to see the ground like we can in the pic.

NZConvertible

That's only necessary if the factory one is gone (your photo doesn't show in front of the radiator).
Do you still have the undertray to put back on?

COsborne

I dont see why I would have taken off the undertray (even though its SOOO much easier to get those dropped bolts)...I guess the problem began when the shroud was removed...

Im going to make a new undertray tomorrow

rx_7_driver

i don't get this i have a 90 n/a and i pulled my under tray off to change my oil cooler lines and did not put it back on and my car is running cool that before
can anyone make sence of this?? i also got a TII hood on the car ( i know there was already a thread saying that there is to little air flowing to help keeping the car cooler), but sence there is no under tray would more air be able to flow to help cool everything off????)
i can't figure out y its running cool than before becides that i don't have the tray on anymore
anyone know y?

NZConvertible

Maybe a blockage in an oil cooler line wasn't letting enough oil into the cooler. This extra heat in the oil would add a load to the radiator cooling system. Just a guess...
You should reinstall that undertray though. Remember, air takes the path of least resistance. If you look through your bumper intake, you'll see that without the undertray, that path is not through the radiator!