My RX7 is getting hot on the highway..
I have a 160 degree thermostat in right now. To give you an example of what it does, today is about 85 degrees F. Driving in 4th gear in town at 35mph my car runs about 1/4 on the temp gauge. At 60mph in 5th it runs about 1/2 even slightly over half.

Im confused about what could be wrong here, seeing as how i have the cooler thermostat installed, and its got new coolant in it.. No external leaking seen.

If it makes any difference, the thermostat pin is facing sideways not up like recommended..

 

Im having the exact same problem. Its bugging the crap out of me. I was gonna replace the radiator cap and see if that did anything. Other wise it would be full flush new pump and then new thermostat I still have the stock shroud and fan.

 

Well i dont know what to tell you. I have a new radiator cap and mine still is getting hot, coolant level is good, it is getting pressure.

 

Do you guys have your undertrays installed? It makes a big difference.

Also a cooler stat can cause issues as well as installing it incorrectly.

 

I dont even think mine has an undertray... Could you show me a picture of that that looks like on a first gen?

 

Its a galvanized tray that covers the bottom of the engine bay from the
under the radator back to the crossmember. If you can look down in front of your
motor between it and the radiator and see the ground you don't have one.

 

I would agree the undertray could be a reason as it is designed to bring in cold air from the road directly to the radiator and engine compartment.

As also stated sometimes a "cooler" rad cap is not a good thing, you need to just get the correct one. But..seeing as you are getting HOTTER when traveling at speed, I am thinking maybe fan clutch or water pump? Those are the only 2 other things other then needed a new radiator. Also, is there any blockage in front like a piece of paper or something?

good luck with it....

 

Hahaha, I have one but its not installed. Can that really be the problem?

 

YES!!! if the problem is at idle/ slow speeds it could be your fan.
if its crusing then its not the fan as air is being forced through the rad, air ducting ie: undersheild is verry importent.

and your coolent mix should be no more then 50% antifreez.

 

new coolant is fine BUT when was the last time the rad was pulled and chem-dunked for a proper flush. new coolant doesn't help a rad that hasn't been cleaned/rodded out in 20 yrs!

Stu Aull
80GS
Alaska

 

I would use the stock mazda 180 degree thermostat with the pin facing up, but that should not cause the car to run hot at speed. I agree with the last two posts. Install the tray under the engine compartment. Replace or have the radiator professionally cleaned (not just flushed).

 

Yup - overheating at speed is about the radiator core getting clogged on the inside.

The fixes for this is either 'rod-out' (where they unsolder the top tank and run a brass rod down the cooling passages to push out crap), boil it out, and resolder the top back on - giving you essentially a new radiator barring any internal corrosion. Either that, or buy a replacement radiator and install.

The problem is that the engine is working against a load at speed, turning higher RPM's, and the fan clutch is normally freewheeling, so the only cooling air you'll get is from the airdam under the nose. An undertray helps direct the air into the radiator, but won't fix a radiator that's overheating due to crap gumming it up.

I've had my 84SE radiator rodded out and boiled about twice in 208k miles. The local shop does it for $60 and even repaints it. Good luck,

 

Clogged radiator.

I've run mine without the undertray for years, and have never had a heating issue....




.

 

One amplifies the other, would be my take.

If your radiator's in good shape, you can probably get by better without the underpan. But if your rad's marginal, and you've also got impeded airflow due to no underpan, the two conditions are additive.

If you have an underpan, there's really no reason not to have it on; it doesn't even weigh much - - really thin sheet metal, just enough to direct airflow.

Today, they use plastic that's actually heavier, but cheaper to form.

 

You shouldn't see your temp gauge move once the engine is up to temp (well only a tiny bit). Which makes me think that the thermostat isn't right. But it's likely your radiator is plugged as well... it may not be the internals that are plugged, but the fins for air to flow around being bent / corroded / uneffective.
Good point on the cooling fan clutch as well. You can get a 2nd gen fan to fit but in either case find one at a junkyard. you can also 'hard wire it' by playing with the bi-metal strip that is on the center of the fan. I forget which way it moves to engage the fan, but you can pull that off and experiment a bit.

 

all true........ but this can change things a bit to,

iowa
Pikesville, Maryland
Huntersville, N.C.
LA
Phoenix, AZ
SW Florida
alaska
Phoenix, AZ
Grand Rapids Michigan
Chino Hills, CA

 

Yeah so you should listen to all of us in the warmer climates, we run into these things all the time

 

Good point. However, if the issue was related to the fan or the clutch, then he would be having problems at idle and low speeds, not just on the highway...

 

When the fan clutch goes bad, it is designed to lock up.

Bad fan clutch will not overheat your car.

 

... unless the plastic fan reaches out and cores your rad after the clutch locks up...

Never seen that on a -7 yet, but my high school friend Tom's 240Z did that one night on Dodge street in Omaha, when he was being frisky with it... Made an awesome noise.

 

Okay - interesting banter about fan clutches aside,...

Those of us that live in places where it routinely hits 115-120F seem to agree that it's because the OP's radiator is clogged.

If he gets it boiled and rodded-out, it will fix this issue. The boiling is to remove all the dead bugs from the fins, by the way.

 

I thought that's what the AC condenser was for??

 

yes.... and install the under shield if its not in place.