Car is an 87.5 GXL auto to manual swap.

This issue has plagued me since I have owned the car. I have tried every thing I know, and every thing that I have found through searching the forums and talking with rotary friends who know quite a bit more than I do about these engines..

My engine never reaches operating temperature. On the stock gauge, a quarter never happens. An eighth is more like it.. barely into the 'operating range' of the gauge. I finally got around to installing an aftermarket coolant temperature gauge, currently (temporarily) installed in the rear iron to thermowax hose. My heat has never worked. In the summer, it does feel warmer than ambient air, but certainly not what I would call heat. The radiator hoses never feel nearly as hot as I know they should be, historically speaking. I have been through four or so thermostats, two of which were Mazda, one 'Duralast' and one A/C Delco.. All OE temp, all with jiggle pins. I've bled (with the heater valve fully open) the cooling system each time, I run an appropriate mix of antifreeze to water, and I know the thermostat is installed correctly. This is my sixth FC from over the years, and I simply do not understand what is happening at this point.

The radiator, pretty much every hose, and thermostat are all new. I do not have an A/C condenser as the car no longer has the system. I have an under-tray, top side OE relay panel, etc. The fan clutch is not seized.

My temps according to the new gauge I imagine are 10 or so degrees lower than real temp due to sensor location. If I turn the temp slider to cold and let it sit for half an hour or so, it'll read 169-170 degrees Fahrenheit. The same scenario with the heat on, but no blower, it'll read around 161. While driving, 'heat' on, temps show 154-156. With the temp slider to cold and driving around, I'll see 160ish. Does not matter how long I drive it for, these are horrible temps to see. I am curious to see in the spring/summer what it reads, but by the same token, the factory temp gauge shows the same readings when it's -4 out or 80.

Who's got an idea?

 

Questions, stock or replacement radiator? Same with the water pump

Have you ever "flushed" the cooling system?

 

My car has ran cooler than factory ever since I got a copper radiator to replace my busted stock aluminum one. I still have the condenser and all of the panels and undertray. Also running an OEM mazda thermostat with the jiggly pin.

I have an S5 with the notoriously inaccurate temp gauge. Even so, my car takes twice as long to warm up than before and the needle reads two needle widths below what it did before and does consistently (within the margin for error on the gauge but its consistent).

I do have heat though, so even though it runs slightly cooler, I can still stay warm in the winter (if I drive long enough for the bastard to warm up!).

Edit: Oh, and my fan clutch works properly.

 

there is a guy in the 1st gen section with the same problem, overcooling. we told him it was impossible, because rotarize run so much hotter than piston engines.

it turned out that his oil cooler thermostat failed. try blocking off 1/3rd of the oil cooler, cardboard works fine, and see if that changes anything.

new oil cooler thermostat is about $95, probably a dealer only part

 

Water pump I am not sure about. But the radiator is a spectra premium. Not sure what the core is.. might be copper. Problem predates radiator replacement tho.

 

Its ideas like this that make me smile upon the forums. I'll throw my car up on the lift at the end of my shift and cobble something together.

Jj, what exactly is cooler than factory, numbers wise...?

 

2 thoughts to build on the oil temperature idea

the stock oil cooler thermostat opens at 150F AND there is a thermostat for the rotor cooling jets that opens at 140F. The rotor cooling jets are like piston squirters on piston engines.

This is a greatly misunderstood part. People call it the oil thermopellet, and you'll read stuff about oil pressure problems, failed this and that, whatever. So people delete that in an engine build because they are terrified that it will fail, when in reality you can just buy a new one from the dealer and unless you are extremely unlucky it will never cause a problem.



also see my thread on the subject https://www.rx7club.com/2nd-generati...tupid-1017659/

I recommend you replace the rotor cooling jet thermostat, which was probably deleted a long time ago, and the oil cooler thermostat.

 

this one is very easy to diagnose it turns out. when the pellet is cold (i'd say open?), oil pressure at ~3000rpm will be in the mid 40's, when the oil is warm (pellet closes the passage), oil pressure should be up at 70psi.

so it can be diagnosed without even opening the hood

 

Put a bit of cardboard in the way. May not be going anywhere else tonight so I will know tomorrow if it did anything.

As for oil pressure I am fairly certain at 3k it is always above 40psi. Ill verify that tomorrow as well.

I should also add that it does not appear to me as if this engine has ever been rebuilt. But no one really knows how many miles are actually on the car/engine.

 

Blocking off significant portions of the oil cooler or radiator does not appear to have any effect.

 

Check if the bypass hole below the thermostat has a plug installed or is welded over. If so, the thermostat isn't doing anything and water is always flowing to the radiator.

edit: I'm not sure exactly how this would work if there is a plug and an thermostat, but it's something to look into.

 

I know exactly what youre talking about, and sadly it is not blocked.

 

Read the posted thread on the oil pellet. Last year I was forced to replace the front main with the engine in the car. I wedged the clutch all the way in for the entire duration of the project. We did heat it a bit. From memory I want to say there was a pin sticking out of the eccentric shaft. Whether or not it has any sort of rubber left I do not know. I didn't really know what it was, so I didn't touch it and made sure it was there when I put it back together. It could be bad for all I know.. but I have doubts in my mind that it would cause a 40 to 60 degree absence of operating temperature.

 

No one has any more theories ?

 

Did you try the oil pellet idea?

 

What do you mean by try? Dont have the funds to replace it at the moment.. but in terms of oil pressure... at three grand it pretty much sits around 60 ish hot or cold.

 

My idea is that you need a real water temp gauge before you can accurately diagnose/troubleshoot cooling problems.

Basically, at this stage, with the stock gauge, I don't believe you know what the temp is and until you do, this is kinda pointless.

 

I do have a 'real' temp gauge. Says so in my first post.

 

So it does.
Clearly, I suck.

 

Yes, and a tight one at that

ANYWAYS, if your unsure about the waterpump, it could be the culprit, back in the day, they had different water pumps if you had A/C or not, A/C having more fins so it would push more water

See where i'm getting at with it?

 

I see what you're getting at.. assuming the engine is the same from when the car was built/an automatic, it definitely had air con as a GXL. I've never seen any options for water pumps for these cars, though. When I said I was unsure of the pump, I meant brand wise or when it was last changed.

To any engine builders, is there anything cooling system related, internally, that could cause such aggressive over cooling? Like a particular way a coolant seal fails?

 

I can't imagine the scenario where a "failure" in the cooling system causes it to run overcool.
My Z car had a custom, ex-racecar radiator and I had to cover about 3/4 of the core to get her up to temp...how much did you cover when you tried that?
Also, you might try disconnecting the fan and run without, see what happens.

 

I'm going go ask the seemingly-obvious question here. Are you sure the thermostat is there and 110% positive it is not stuck open? To quote Aaron Cake's e-fan article "it is the thermostat that regulates engine temperature". Disconnecting the fan won't change anything because it is riding on a thermo clutch which varies fan speed like a torque converter. If the fan is stuck due to clutch failure, it can over cool as well.

Also, every S4NA uses the same N326 water pump. If yours is sketchy, call Ray Crowe at Mallory Mazda for the first cousin hookup on a Mazda remanufactured one, the only kind you should ever use.

 

I personally am absolutely certain that my current thermostat... and every other one I have had in the car work perfectly. Tested in water with thermometer

 

Okay, just wanted to make sure the most obvious items were covered. This sounds like a seized clutch fan, in that it is always pulling air through the radiator and 'fighting' the thermostat. I can't say with absolute certainty as I've never experienced this myself (mine leans the other way thanks to a 20B-REW lol), but this Z-car article makes sense of it better than I can: Here are the instructions:

To determine if the clutch is seized, the only method I know of would be to try turning it by hand and watch if the water pump moves too. A seized one will move perfectly in sync with the water pump.

Aaron Cake, could you please weigh in on this and double-check me?