It's been a hot summer in Sacto this year. But reading through all the posts on coolant temps it seems that my FD runs hotter than others. I've done every mod out there. Fluidyne radiator, new t-stat, Autometer Sportcomp temp gauge connected to t-stat housing, Redline Waterwetter w/70% distilled water, fan mod, miata fan switch, new hoses, aluminum AST, new caps (13# on AST) and bypassed T/B coolant line.

Temps:

Cool mornings (60-70F) freeway cruising at 70-80++ mph. Temp is 190-195F. Fans on all the time. With fans off on the freeway temp creeps up over 195.

Hot afternoons (90-100+F) w/fans always on. Temp is 210. The faster I drive (80+) it gets hotter but not higher than 230F on the gauge.

City driving in hot weather with fans on: Baby it/no boost it always stays around 210F. Boost it and temp goes over 210-230 but settles back down to 210 when I baby it again.

The autometer gauge has no hash marks between 210 and 230. So above 210 it's hard to say what the temp is. I don't dare run the A/C on hot afternoons even cruising on the freeway. It definitely goes about 230 with a/c on. With out A/C it still goes above 210 and sometimes will hit the 230 hash mark on real hot days when driving >80mph. But it cools down when I slow down under 70mph. ...and yes I always run with the fans on . With all this the stock gauge never moves above "normal" so I guess that means temp never got above 230 right?

Questions:

Is the Autometer "sportcomp" gauge very accurate? The hash marks are 180, 195, 210, 230 and 250. When the gauge moves after engine warm up it goes right to about 185-190 which is where t-stat opens right?

At freeway speeds my car still runs cooler with the fans on versus the fans off. Also the faster I go (80+) it runs hotter. This is higher cruising speed and not driving hard (no boost). Seems like the higher the RPM the hotter it runs. Apply boost then temp ramps up real quick. But you would think there would be enough air hitting the radiator at high speed it wouldn't need the fans. But mine does. Why?

So, is my car running at "normal" temp? Or too hot? Any suggestions why? Everything else is normal, checking coolant level when cold, it's always full, when hot there is no girgling noises. When I get home every night I always pop the hood to let the heat out of the engine bay. It's always hot as hell under the hood but otherwise there's nothing to indicate it's overheating. Other than that it runs great, has good power and no smoke at all. It just does not like hot Sacramento summers and me driving fast! I'd like to hear from others who live in the same weather conditions. Hot dry heat like the California valley.

Thanks for your comments!

 

here's my sig with mods.

 

Make sure there isnt a way for air to get around your radiator. At speed your car should not heat up like that. I live in florida and i've done LONG boost runs down the interstate in the afternoon with the autometer guage staying at ~195.
My mods include a downpipe and an intake.

 

I have exactly the same experiences are yours. In fact, at Buttonwillow yesterday, I couldn't go for more than a few laps without getting too hot -- I was pegging out water temp at 230F (PFC read 105C, so block wasn't that hot) and oil temp at 260F on a 95-degree day. This is the fans running high speed from 92C and up.

My mods are in my sig (with a brand new T-stat). I think the next course of action is to fab up shielding for the sides of the radiator (like everyone says to do ).

Good luck and keep us posted.

 

Forgot to mention I stuffed foam on the drivers side of the radiator when I installed the Fluidyne.

The passenger side has the airbox baffle sheet metal. I tried a test today. It was over 100F dry weather today. I gritted my teeth on the way home and managed to keep it at 70 mph steady for about 15 minutes. Temps stayed steady just above the 195 hash mark. Probably about 200. But then going up a hill (the big I-80 bridge going over the Sac river) it creeped up more. Then I tried cruising at 80 and it creeped up to 215 and held there. Then I had a stretch on I-5 to go faster on so I cruised for a few miles at 90mph. It went over 215. About 220 my guess. Then when I took the exit it dropped just below 215 and stayed there driving home slow on streets. All this and no boost applied at all and fans on high the whole time. Either I'm still not getting enough air to the radiator (a/c coil clogged maybe?) or something is up with the water pump or maybe the new mazda t-stat I put in is bad?

 

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If your temperature gauge is accurate then you're definitely running too hot under those driving conditions, so your right to be keeping a close eye on what is happening.

When did the higher temperatures first start to show? Before or after you added the new radiator and cooling modifications? If after, then the thermostat you changed may possibly be at fault, but its a long shot.

Are you certain that your temperature gauge is accurate? The way you explained your temperature readings versus driving patterns it seemed as if your temperature gauge was reacting too quickly. Is your temperature gauge sensor fully under liquid or could it be partially reading hot vapor? Are you checking the coolant level at the AST to make sure it is full?

Are there any kinks or restrictions in your major coolant hoses such as in and out of your radiator?

Have you actually observed your radiator fans running to be sure that both are working? Could the wiring to your radiator fans somehow be reversed so the fans are running backwards i.e. pulling air from the engine compartment into the radiator?

Is your belly pan in place so that air is being diverted from the underside of your car to your radiator?

 

All the mods I did (radiator, thermostat, gauge, hoses, ast, etc) were all done at the same time. So all I had to go on before was the stock gauge which we all know is worthless. I'm ok on all the stuff you mentioned but maybe the sensor location. I drilled/tapped a hole in the t-stat housing (per robinettes page). The metal there is pretty thick and only a small portion of the sensor sticks out into the coolant. But it still gets surrounded with coolant and doesnt touch metal. Yes AST is always full too. So besides checking the a/c coil to make sure its not clogged I'll try a different gauge. One thing for sure I confirmed thanks to this forum is I'm running too hot compared to others. I'll post my solution if/when I find it. Thanks!

 

I know you have already heard this, but I would replace the thermostat. Check the manual to make sure it is installed correctly. Then change the gauge if you are still running hot.

 

I'd make sure you have all the air out of the cooling system, then check the thermostat and then the water pump. You shouldn't get temps that high with the fans running on high.

 

You do still have your undertray on, right?

I didn't put mine back on after replacing the radiator.. Fine during March and April, but come engine rebuild time (not due to cooling) in June/July, things were hot.

100+ degree days here in TX, I had the same symptoms as you. It'd be fine driving around town, but the minute I took it over 80 mph on the freeway temps would just start to rise immediately.

Got all the air out of the system, still did it. Put the undertray back on and now I don't see any water temps over 92c on the pfc, even when sitting in traffic for 30 minutes. Intake temps are another story tho...

 

Agreed, the stock gauge is not linear and therefore doesn't always provide useful information. However, before you did all the cooling system upgrades were you getting any indication from the stock gauge that you may be having temperature problems (i.e. higher than average readings, fluctuations, etc.)? My point of course is to try to determine whether or not the temperature readings you are getting now occurred before or after your upgrades.

I'd certainly take a much closer look at that sensor. I would think that if it is just barely sticking into the coolant flow stream then it is not getting an accurate reading. The sensor may be "confused" by stagnant coolant nearest the sensor that is subject to heat soak.

 

You can do the stock gauge mod. to linearize it and calibrate it. Requires removing the gauge cluster and making a small box. Very easy, and cool. My stock gauge now moves up and down all the time as the temps change in the engine. I think the instructions are on the San Diego club site.

 

Here's an update:

1) Yes - undertray is on. Always.

2) I drove up to Tahoe on 50 on a warm day (high 80s) and had to pull over twice to let it cool down. I was babying it the whole way too. One time in a passing lane a Prowler was in front of me and he stepped on it. I couldn't resist tailgating up the hill (didn't take much effort). My gauge quickly pegged at 250! My stock gauge started to rise quickly too. So I immediatly pulled over again to let it cool down. After finally getting over the summit it cooled down quick to 180 going down hill. On the way back (mostly downhill), it was at 180-190 the whole way.

3) So last weekend I pulled the thermostat. Tested it in a pot of boiling water. It opened and stroked exactly per the manual. It's pretty new anyway.

4) I pulled the water pump. Having never seen an FD water pump before I immediately thought it was a cheap *** non-OEM water pump with a paddle wheel impeller (not a nice cast impeller like my 81 RX7 had). So I ordered a new Mazda water pump. I got that today and it looks exactly like the one I had!

So now I'm really stumped. What the hell is wrong?

The only thing left I've read is the trapped air problem. Where does air get trapped and why? You would think after a few months it would purge itself out. I have no leaks. Coolant in AST and in t-stat housing is always full when I check it (engine cool). I know it's not the gauges now since the stock one went up too (3/4 before pulling over with autometer gauge at 250).

Thanks in advance for you comments.

 

That's too bad that the water pump was the same. Does the new pump have a pulley, or do you use the old one. It's possible, but unlikely, that the old pulley is too small.

I still suspect that the thermostat isn't opening all the way when you drive the car, or it was installed improperly. I suggest that you buy a new one, and check the manual for proper installation instructions. They don't cost much. Maybe you can sell your extra water pump to help pay for it......hahaha

 

Your Radiator might be clogged up or corroded inside. I was seeing really high temps as well. 240-250 F !! I also recently switched to EVANS Coolant so it is normal to run a little hotter than regular water and antifreeze, but not temps as high as I was seeing.

At the suggestion of my mechanic, I installed a Koyo radiator. My temps now are a rock solid 185 F maybe 195 F in stop and go traffic.

The Koyo is huge, its almost twice as thick as the stocker. I had to add more than half a gallon of coolant more after the swap...

 

Well, being an FC guy I dont know how well this applies but im also a Koyo user and max temp I see on hot days here (+90F) is about 87C with a norm of 85C. Nights I have an average of 80C and max of 85C. The Koyo also dissipates the extra heat very very quickly.

 

Pressure test system (tee into sat line with pump and gauge), could be leak at caps. Must hold pressure, or will boil near 215F.

Should also seal sides off the belly pan.

 

I might have some insight on this issue. Have you had your engine rebuilt recently? Did you ever notice this happen with the stock radiator? The reason I ask is because I had a severe problem with my Fluidyne radiator as well. I am in the process of getting a new one from them as we speek. I just had my engine rebuilt and was ao but 3500 miles ont he new motor on my way home from Delaware when I noticed that every time I got over 60 mph the PFC started to rise. It made it to 105 a couple of times and I immediately pulled over. The car was fine under 60 mph, so I couldn't figure out what was wrong. I had the AC on for the fans and turned the **** all the way to hot to move air over the heater core. It made it back to Charlotte, NC but not much further before the new motor bit the dust. I took to my mechanic figuring it might be his fault. Come to find out we put a stock radiator back in after the new, new motor was put in and the problem stopped. Since the radiator wasn't a year old yet we sent it back to them and they still couldn't find anything wrong with it. So I attempted to put it back in again and bam same prob.

They just took possesion of it again and are issuing me a new radiator for free. They cut it open and from what they can see the radiator had some of the engine sealant inside the radiator coating the fins so it was being insullated from the inside out and therefore keeping the heat in. They think this was the cause but they are not 100% certain. I am debating putting the new one in or just selling it and keeping the stock unit which has made it all summer without a flaw. Maybe this will help you, maybe not but it is sure nice to get my story out.

Good Luck!

 

Did your overheating problems first start before or after you did the cooling system mods?

If after, then you need to focus on your mods and workmanship because somewhere in there you caused the problem.

You said you are frequently checking the coolant level. Is the coolant level going down and/or do you see any "contaminants" floating on top of the coolant when you check the level?

You said you installed a Fluidyne radiator. If it was a used radiator it could be clogged.

Assuming you have done everything correctly and there is no evidence of leaks or contaminants then I agree that the next step in diagnosis is getting a pressure test on your coolant system.

 

This is really interesting. That may have been the cause for my excessive temps... I had just gotten a rebuit motor installed and started to see the overheatingwhile I was breaking in the motor.

I wonder if any other guys have had their radiators get clogged from engine sealant after a rebuild...

 

If by sealant, 'yall mean assembly gunk, I have seen a pretty large amount of what looks like vaseline in my coolant overflow tank and floating in the filler neck after my rebuild (Pineapple). And come to think of it, the radiator doesn't cool down as quickly as it used too (Fluidyne, in there B/4 and after the rebuild). Hmmmm...

 

Not really an answer to your problem, but when the temps get really high you can turn on the heater to help cool it off. I know it sucks sitting in the car with the heater on when it is over 100 outside, but set it on defrost to direct the air away from you and just sweat it out.

 

I don't think it's sealant. It's got the original engine with about 72k miles. I installed the radiator and other mods about 5k miles ago. ....and before I did all these mods I didn't have the autometer gauge so it was hard to tell how hot it was really running. One time (before the mods) on a trip going up a hill in warm weather the stock gauge did go up to almost hot but that's the only time. Last year when I drove to 7stock (no mods yet at that time) we drove in bumper to bumper traffic with the a/c on and the stock gauge didn't move. So maybe there is something wrong with this Fluidyne radiator. W

Also I doubt its my workmanship. I've owned rotaries for over 20 years and rebuilt a few too. So swapping a radiator and hoses and stuff is not high tech work for me. But the comments about a clogged radiator seem valid. Maybe it's got junk in it from the manufacturer. Maybe the welder had a bad day and decided to weld up a bunch of the tubes closed. Wish I had a boroscope to peak inside without taking it apart. Maybe the coolant jackets in the motor are scaled bad. I'll pull the radiator and have it inspected at a radiator shop and get it flushed out. Then I'll put the new water pump in and new thermostat I bought too and see what happens. Hopefully that will do it.

Thanks for the suggestions!

Oh yeah regarding the vaseline "spurvo" mentioned...yes it's used to hold the water O-rings in place during engine assembly. ....also regarding my coolant level. It's always full when I check it. It never needs a drop of coolant.

I'll post an update soon. Thanks!

 

Hmmmm...My rebuild was done by Pineapple too.

RX7 8U, Have you topped off and "burped" your cooling system? What I mean is fill the motor with water/coolant at the filler neck while having the small coolant hose off at the UIM/TB. That way all the air bubbles are forced out of the system to the highest point in the system, the TB coolant hose. Whoops, I just noticed that you bypassed the TB coolant hose.

Maybe there are air bubbles stuck in your cooling system.