I replaced quite a few of the cooling system elements on my FC RX-7 non-turbo. I replaced the stock radiator (with plastic endcaps) with an all-metal aftermarket radiator (i think it, the water pump with an OEM-remanufactured unit, the upper and lower radiator hoses, and the coolant level sensor. I added a 60/40 mix of distilled water and green antifreeze. Unfortunately, the engine seems to still be running hot. The temperature gauge should read at 1/4 of the gauge for normal running, but it doesn't stabilize until 1/2 of the gauge now. I took it for a 30-mile trip with both highway and street driving and the temperature seemed to stay stable at 1/2 gauge. There is no leaking. I think I burped all of the air out of the system.
Any ideas as to why the car is still running hot? Am I not using the correct water-to-coolant ratio? Would the aftermarket radiator be less efficient than the old stock radiator? I'm worried because I need to get my Mazdaspeed3 to the body shop and will need the RX-7 to get me to and from work. It was OK today on a cloudy 71deg F day, but I don't want to damage my engine on a 90+ day like we've been having recently.
IIRC when I had an FC, the supposedly common knowledge was that the stock gauge wasn't that great and only served as an 'engine cooked' indicator.
You might be better off verifying the actual coolant temp with a decent aftermarket gauge.
RexSeven,
I am running Prestone 50/50 in my '88 FC. I doubt that is your soultion.
A few thoughts...
Make sure that the fan belt belt tension is correct. From what I have read you need to run both belts...i.e. don't disconnect the air pump. How is the fan clutch...check the play. Is your coolant fill boss (the one at the top of the thermostat elbow with the pressure cap) the original plastic one? Mine was and was cracked. I replaced it with the aluminum Mazda replacement part. Got it from Mazdatrix. Did you put all of the radiator shrouding including the undertray back in place? Where is the air bleeder on the new radiator? Near the top hose like the OEM uint? When you filled the coolant system did you move the heater slider to hot and let coolant come out of the radiator air bleed to ensure it was full? When you burped the system by running the engine with the coolant fill boss pressure cap off are you sure you ran it long enough to let the T-stat open? Did you change the T-stat or remove it and re-install it? You have to make sure the pin is in the right orientation. From what I read don't use anything but an OEM Mazda T-stat. I got mine from Mazdatrix. Good luck.
-Ray
Been here before, at least once. Doesn't sound like an airlock but ya neva kno. 
T-stat would be a good place to start. Next check the accuracy of the indicating system. I've had that problem once......or twice. An aftermarket gauge system fixed it once, a sending unit fixed it the other time. (2 different cars)
racer_ace wrote:
Make sure that the fan belt belt tension is correct. From what I have read you need to run both belts...i.e. don't disconnect the air pump.
Belt tension is correct and I'm running three belts (air pump, water pump, alternator). I removed the A/C belt since the A/C didn't work in the first place.
racer_ace wrote:
How is the fan clutch...check the play.
I checked it, and I think it's OK, but I will double-check.
racer_ace wrote:
Is your coolant fill boss (the one at the top of the thermostat elbow with the pressure cap) the original plastic one? Mine was and was cracked. I replaced it with the aluminum Mazda replacement part. Got it from Mazdatrix.
It's plastic but there are no cracks. It leaked before I installed the new radiator but a new fill cap fixed that.
racer_ace wrote:
Did you put all of the radiator shrouding including the undertray back in place?
Yes. I did notice the original radiator had a foam strip underneath that went between the radiator and the undertray, which the new one lacks. I will make a new one, but I will need to buy some foam since I have none laying around and the original is deteriorating.
racer_ace wrote:
Where is the air bleeder on the new radiator? Near the top hose like the OEM uint?
The new radiator does not have one. I've been burping the coolant by removing the radiator pressure cap, overfill hose, and coolant fill cap.
racer_ace wrote:
When you filled the coolant system did you move the heater slider to hot and let coolant come out of the radiator air bleed to ensure it was full?
Yes to the heater, there is no bleed screw.
racer_ace wrote:
When you burped the system by running the engine with the coolant fill boss pressure cap off are you sure you ran it long enough to let the T-stat open? Did you change the T-stat or remove it and re-install it? You have to make sure the pin is in the right orientation.
I don't remember if I left the fill cap off or not, but I will try again. I didn't touch the T-stat. The T-stat was replaced within the last 3000 miles with an OEM unit and was working since I could feel the upper radiator hose getting hot.
I ran out of daylight so I will have to try everyone's suggestions after NEFR is over. I'd rather avoid installing an aftermarket gauge because I plan on buying either a strippo or turbo FC soon and selling the current one once the performance parts have been swapped to the new car. The MS3 only lost some front bumper paint to a blown-out semi tire so there is no rush to get it repaired.
I took the RX-7 to work today since the MS3 is not in great shape. It's still running hot. I tried burping the radiator again but it looks like I already got all of the air out of the system. I checked the belt tension again and it looks fine.
I'm beginning to think the RX-7 doesn't like this particular radiator. The OEM radiator appears to be aluminum with a plastic top endcap while the aftermarket one appears to be all brass including the endcaps. I'm still going to replace the fan clutch and add the foam strip to the bottom of the new radiator to see if it make any difference, but if I don't see any change, then I will reinstall the old radiator.
I would think a radiator themometre would be cheap thing to have. Either infrared or even an oldfashioned between the fins style.
As for the gage.. I thought most cars had the gage in the middle for optimal running temps? every car I have owned was like that
According to this site, that's not the case on the S4 RX-7s for some reason. The S5s moved the normal temperature range back to the halfway point but is much more inaccurate than the S4 gauge.
http://www.aaroncake.net/rx-7/buy1.htm (scroll down to "Overheating/Temperature")
As for the radiator thermometer, I'm not sure if that would be in the best place for getting temperatures since it is a heat exchanger. rx7club.com posts say the best place to mount an aftermarket water temp. gauge is on the water pump housing.
not talking a gage for the interior of the car.. just a diagnostic tool for for checking to see if the car is indeed overheating.. like a handheld infrared pyrometre
I've pretty much narrowed it down to the radiator. I did some research on radiator materials and it looks like brass isn't as efficient at cooling as aluminum. The old radiator is going back in sometime after Monday when the MS3 is repaired.
RexSeven wrote:
I've pretty much narrowed it down to the radiator. I did some research on radiator materials and it looks like brass isn't as efficient at cooling as aluminum. The old radiator is going back in sometime after Monday when the MS3 is repaired.
I've always heard brass had better heat transfer than aluminum, all else considered equal. Aluminum is just lighter.
Are you sure that the thermostat is opening all the way? Just a 1/4" to little can mean a large difference in how much coolant is going through.
Take an infared gauge and make sure that the temps are uniform across the face of the radiator. Maybe it aint flowing as well as the old radiator. Fancy dont always mean that it is efficient and maybe that explains why it was so cheap on the internet.
What year is the car? I had an 88 that did the same thing when I replaced the radiator with one that had no bleeder. I put one of the thermostat housings on it that has a cap and bled it that way. It looked dumb with two radiator caps but it quit running hot.
Kia_racer wrote:
Are you sure that the thermostat is opening all the way? Just a 1/4" to little can mean a large difference in how much coolant is going through.
The thermostat is relatively new and it is opening - I can feel the upper radiator hose get hot.
Just to give an idea of what I was trying to do, below was how the temperature gauge behaved with the old and new radiators. The new radiator was an OEM equivalent to keep the car SCCA E Stock legal. 1/4 gauge is the normal operating range for an S4 RX-7:
Old radiator: 1/4 gauge most of the time. It would slowly rise up to a little over 1/2 gauge when I drove it hard (i.e. at autocross) or during highway driving on hot, humid days. The whole idea behind all of the cooling system work was to reduce those spikes, though I was told by an old rotorhead that that may be normal behavior for S4 RX-7s.
New radiator: 1/4 gauge when cool out (at night), consistently at 1/2 gauge when hot out, a little over 1/2 if driven hard.
bamalama wrote:
What year is the car? I had an 88 that did the same thing when I replaced the radiator with one that had no bleeder. I put one of the thermostat housings on it that has a cap and bled it that way. It looked dumb with two radiator caps but it quit running hot.
The car is an 87. It has a fill cap on the t-stat housing and a pressure cap on the radiator. It does not have an air bleed screw.
