I've got an '85 GS with the stock 12A in it. I just got it back from the dealer today because I brought it in for a general look over as I just bought it. They replaced the radiator cap in house while it was there, it was overheating a bit when I brought it in. Drove it home slightly hard once things warmed up to make sure it was ok. The entire way home, didn't crack past 1/3 on the temp guage.

Got home, was going to take it out for a drive with the wife, about 5-10 miles the temp got past the half way point and was approaching the red line pretty steadily, dropped off the gas and let it coast to keep some air flow over the radiator, temp dropped back to just below half.

The entire ride home it never went lower than that and crept up any time I went over 3k on the tach. During this time there was no overflow. What could be causing this? I know the coolant is dirty and getting flushed out in the morning and fresh put in and an oil change is coming up probably wed as I won't be driving it tuesday. Sounds likes the water pump tested ok when they had it in shop as well.

I've searched for some general solutions to this problem on the forum, but the radiator cap is the only one I've found so far, is it possibly something else that I'm missing? Does anyone have any suggestions?

 

Im not a professional on rotaries, and I might be wrong.

But, I think its your fan.

Ive heard that the fan is for when the car is not moving (or idle).

but I could be way off.

 

oops forgot to add that, fan runs fine during idle and you can tell when the fan clutch kicks on during driving, it seems to work ok. I could be wrong, but I believe the fan is built right onto the main shaft.

 

Well it might be the fan. If you drive it past 30 mph and the temp doesn't go back down to normal range, then it's not the fan. Other possibilities: thermostat, clogged coolant system.

 

Temp will not really go back down to the 1/3 mark past 30 mph, it goes up at this point if anything, depending on what gear I'm in.

On the cooling system being clogged, how much an effect would old coolant have on this, would it be this pronounced?

 

I would suggest that since you are going to Flush the Cooling system anyhow,is to replace your Themostat as well(with an OEM).you said NO overflow,did you have any coolant in your Overflow for the System to Take,if the Coolant in the System gets Low?(minimum and Maximum on the Overflow bottle)?also what did the Dealer Replace the Rad cap with?(was It OEM?)..what I am suggesting is to Flush/Fill the cooling system,replace the Thermostat and Cap..make sure that there is no air in the system,THEN see if your Gauge indicates the Flucuation that you are talking about.If everything is OK,then the Gauge should reflect that.Also check your Fan Belt,and make sure that the Clutch fan is working Properly..Good Luck.

 

Ok so it's not the fan. Check the thermostat to make sure it's not malfunctioning. Next, you might need to service the radiator or, ideally, replace it.

 

What's the best way to test that the fan clutch is working properly? It sounds like a small tornado when I rev it while it's hot and it looks like it is turning as engaged. All the belts have good tension on them as well.

It was a mazda dealer, so I hope the cap is OEM, I could be wrong on that one. I'll have to pick up a new thermostat tomorrow and do the flush and replace then.

Followed the instructions here on the fan issue and it tests out ok according to that manual:
http://www.wankel.net/%7Ekrwright/files/manuals/1985_RX7_FSM/85RX7(3)cooling.pdf

 

It's not the fan and it's not the clutch or anything related to that. If it was, driving at higher speeds would lower the engine's temp.

 

Mkay, sounds like a thermostat swap and a coolant flush, one last dumb question until tomorrow when all this is done, is it ok to use plain old water to flush out a coolant system?

 

To flush it, yeah, but at the end make sure you use anticoolant fluid. I actually like to use pre-mixed anticoolant, so I don't have to worry about proportions or what kinda water I use.

 

Yeah, I've got 2 gallons of 50/50 pre-mix so I'm good to go there.

 

Well if the last part of the flush is done with that, then I'm not sure if it'll be enough, but you got the idea.

 

take the thermostat out and put it in boiling water, check if it opens or not.

 

Make sure you have an 0.9 ATM pressure cap (best is an OEM from Mazdatrix), and an OEM T'stat, properly installed.

Flushing the system is a good idea. I have mounted a Prestone plastic tee in the lower heater hose on the passenger side to facilitate draining and flushing. Costs about $6 at the autostore. I've done it on all rotaries.

 

Alright, replace the Thermostat on my baby, did an OK flush on the system, temps have dropped dramatically. I can drive around 70 now without the temp going past 1/3 but if I push that further it begins to move up.

Next week I'm bringing it in for a professional flush and clean on the coolant system. I'm fairly sure it still had either the original coolant in it, or coolant that was severly overage and probably some deposits from sitting. I think a good flush should help as well.

I did boil the thermostat in it, it didn't open as quick or as wide as the replacement so swapping it out was definately a good thing.

 

Glad to hear. Good idea on the professional flush.

 

What exactly is considering the ok temp range for the 85 12A engine? I'm usually 1/3 until I get on the highway and go over 70, I've heard different ranges, If I'm between the two inside lines on the temp gauge is that OK? or is the halfmark that everyone talks about a definite problem?

 

It's not good, meaning non-optimal if it goes past the 1/2 mark. Definitely bad if it goes to the last mark, and you can permanently damage the engine if you do that. Everything being ideal, I think 1/3rd of the dial mark is the ideal temp.

 

I hope the coolant system flush works out then and it's just dirty coolant, there's some nasty brown residue that settles out of it from the stuff I did pull(settles to the bottom, not like oil on top).