Temp Guage Rising at Long Idle and High Speeds...
 

1990 GXL; 5 spd; 3k on rebuild; intake; racing beat full exhaust; Koyo radiator

A while back I posted about my temperature guage moving from right below 1/2 to nearly 3/4 after leaving it idling for about 15 minutes outside on a warmer late winter day (60 F). Ultimately, I got a new exhaust system (thinking of clogged cats) that is racing beat and total free flow from downpipe to muffler, and I also put on a brand new Koyo radiator. Yeah, I laid down some cash. Guess what, same exact symptoms... I think my car is on a suicide mission.

If I drive around town a lot, and then stop and the car idles for more than five minutes, the temperature guage wants to move past 1/2. Moreover, if I'm cruising down the interstate, and the tac goes above 3200 (around 85 or 90mph), the temperature guage moves over half. As soon as I take my foot off the gas, it is as if it says, "Okay, just making sure you're paying attention..." and it goes back down below half. Also, another interesting point to note, if I'll slowly accelerate, reach a speed, cruise a bit, then let off the gas, coast a few seconds and raise the bar a bit (maybe five mph more than the previous cruise), I can climb to 100mph under the temperature guage radar. But, if I just go for it, he busts me every time.

Any ideas would be greatly appreciated... I hope the solutions are cheap. Its going to get warm here pretty soon, and when that happens, this problem has to be fixed or I'm screwed.

Car's cooling system isn't taxed at idle stock. Startto change things around and it might be though. Do you have an e-fan or clutch fan?

If you have an e-fan and have i wired through a temp sensor, it might be faulting and not coming online early enough to be effective for idle conditions.

If you have a clutch fan, you're still using your fan shroud (right?). The fan shroud keeps air moving through the radiator.

Also... I think when clutch fan is fail-safe (anyone confirm?) so if it wants to not work right anymore, it should be constantly locked up (always cooling best it can).

The only thing I have changed is the radiator... That's all. I put a new exhaust on it, but to my knowledge, that couldn't be considered part of the cooling system by way of an upgrade.

When the engine was rebuilt, a new mazda thermostat was installed, but a used water pump came with the engine. There are no coolant leaks anywhere. Yes, I am using the factory shroud around the clutch fan, and the clutch fan (stock) still seems to have resistance in it if I turn it when the car isn't running. It is also spinning at idle if I get out and check.

I don't understand what is going on. All I've done is replace a 14 year-old radiator with a new aluminum Koyo. I thought maybe that would solve the problem. However, the same symptoms are here that were also here before the new radiator. Temp rise at long idle; Temp rise at high speeds on interstate.

Temperature Sending Unit??? Water Pump???

You're not alone man. I am having somewhat of a similar problem. I flushed my radiator several times, new thermo and rad caps. Tested the senor...good to go. Stock fan clutch with shroud and has the resistance as well. One thing I did notice though and not sure if it's normal, on my initial start up I can after the fan blows hard for a few seconds and then settles down I can stop it from spinning with my hand and actually spin it the other direction. Now, after the engine warms up I can no longer do it, so not sure if that's okay.

Now as far as your used water pump.....I still have my original one on. Only thing I can think of besides maybe the fan clutch is the water pump not circulating properly. Book has a check on it. Says with engine running to squeeze the main upper rad hose for a few seconds and let go, water pump if working correctly will feel a sudden surge while letting go of hose slowly. With mine I can't feel a damn thing. I took the belts off and felt for play in the shaft, any resistance....and got nothing. So, best thing I can think of for the both of us, is to take off the water pump and inspect the guts and put a new pump in. Unless anyone else has any other advice??? Warmer and hotter days are ahead :eek:

could it be your running a little lean causing the engine to heat up a little..,

i had this problem once when i replaced a few hoses..
check all the hoses around the throttle body and make sure
there's no air bubbles in them...

happened in mine and i was getting the same symptoms

Can the water thermo sensor, if bad cause overheating when driving hard, but cool back down to the half way mark when easing up? Coolant looks nice and green, no air bubbles. Should I be able to see the coolant actaully move when cap is off and thermostat is open if water pump is circulating correctly?thermostat water thermo sensor

Give a good read to http://www.aaroncake.net/rx-7/cooling.htm

But your problem sounds odd....Slipping belts on the water pump? You ARE running the proper two belts over the pully, right?

Are you SURE you properly bled the system? Air pockets can cause blocks wich prevent coolant from circulating...

But it does sound like a water pump issue...how's the impeller look?

Update: After my car threatened me all evening at stop lights, on the interstate, and even sitting in the driveway once, I finally got fed up and went over him again. My exhaust hangers were a little off, and the time away from worrying about overheating was well served adjusting a low idle post exhaust install. But, after that was done, I revisited my 'issues'.

Yes, Aaron, I do have two belts on the water pump pulley. However, one belt is to my air pump, which is no longer viable. I have a straight pipe exhaust (racing beat downpipe to mufflers). I checked under the car, and all of my plastic is completely intact below the car. However, I noticed a large piece of plastic that was supposed to be blocking air from slipping between my nose and my air bay (oil cooler and ac condenser) had been knocked loose. He was hanging out sprawled across my lower grill. Now, I don't think I'm lucky enough for that to be my problem, but needless to say, I ripped that little bastard out with determined vigilance. I plan on going and getting a sheet of aluminum tomorrow and replacing the barrier that once kept air from going anywhere but the oil cooler and ac condenser, which was plastic.

I still think there is more, but I'll push it some tomorrow to see if that was in fact my problem. Also, my buddy brought his seven over, and although I do have resistance in my fan, his has much more.

If it runs hot tomorrow, I'm replacing the thermostat and water pump for sure. Any other suggestions? What about running lean/burning rich? How do I check that?

It's doubtfull that your problem is caused by an improper A/F ratio.

If you are referring to the plastic undertray, then yes, it is VERY important for proper cooling.

Are you losing any coolant? Burning it? Car pass the "bubble test" (search)?

Hey Aaron, yeah both belts are correct. Under belly pan is in tact. As far as properly bleeding system....that is just a matter of topping her off till she won't take anymore and opening the bleeder screw right?

All this overheating for me started after I changed my coolant a few months ago. Since then I have flushed the system twice and replaced all necessary items. But still the same dilemma. So I'm still thinking water pump, maybe impellar is worn out.

check your timming.

did you try pulling off the small coolant hoses around the throttle body and crankin the engine till coolant comes out??

do them one at a time from the line closes to the firewall around to the BAC and afte that

Hey, at the suggestion of a pretty sharp mechanic, I'm gonna install an aftermarket temperature gauge as soon as I can...

Can someone please offer me a cheap suggestion to accomplish this, as well some instruction? Will a universal temp gauge work from, say, Advance Auto (Sunpro)? How do I install a universal temp gauge? And, MOST IMPORTANTLY, once the temp gauge is installed, what are the temperatures that I should be looking for (cold, warm, and "new engine")?

Thanks in advance for bumps...

Getting Warmer

I also have a 1990 GXL..
My temp guage sits just above half on the guage.
Is this normal? Do i have anything to worry about?

Please explain more.

Remeber guys, I am only running hot when I give it some juice, usually in fourth. I slow down and it stops climbing. Could my fan clutch be failing at high speeds? I don't run hot when driving easy or sitting idle. But it is a definate change from before.

Apprecaite all the input fellas :)

my post was aimed to mathetas

Please explain more.


Remember guys, I am only running hot when driving hard, usually in fourth. Goes up to the 3/4 mark. I try not to let it get higher so I either slow down or bust on the heat to bring her down.Could it be that my Clutch fan fails at high speeds? Cause when driving easy, sitting idle or driving on cool nights I don't have this problem.

Appreciate all the input fellas ;)

the fan doesn't do anything while moving. it's for when you are stoped.

Wouldn't the fan be directing air into the radiator as well as blowing air on the engine at high speeds?

Exactly what I'm wondering. Cause I'm only overheating when driving hard in my case.

Thermostat.........
$18ish for the OEM one.

My car would run hot on the highway(I had an aftermarket gauage in) I could see the needle rising as I went faster.


The Koyo can't cool the water if your tstat is blocking the water from entering it.

Replace that anyways. It might fix it.

I replaced the tstat using one from Autozone. Is there really a difference guys? What about a tiny leak coming from the tstat housing, near the eyes? Could that small of a leak cause the high speed overheating?

Well everyone swears by the OEM ones.

I doubt a small leak would cause over heating unless you would take a lot of air in which totally ruins cooling.

I had a failing Tsta and would run temps of 220+ on the highway.

As soon as I put in a OEM unit I was running 180 daily no matter what.

Havik... I tried to pm you again, but the system blocked it for some reason. Anyway, dude, you should definitely go get a Mazda t-stat. It is less than $20 and well worth it - specifically designed for your car. If you can, I'd also think about finding another housing if yours has a hairline crack in it. You know that stuff will expand in the Carolina sun. Anyway, just lookin' out for a brother. I'll let you know how my new clutch fan works out ASAP.

I will add my two bits. Use an OEM and OEM only t-stat for safety's sake and get an aftermarket temp gauge.

An easy test. I think idle temp is ~~ 170 ish (mine atleast). When cold, remove rad cap, toss in the MECHANICAL temp gauge (the one with the copper tube thing with the thing at the end, not an electronic gauge!) where the rad cap goes (far down if possible). Start'er up, watch and learn.. No, nothing is going to boil over/explode (coolant does expand when it gets hot so you'll spill some a-freeze.). That would be your 17 dollar answer.

A faulty ground will do the same thing. Try this. While idling/doing nothing, turn on EVERYTHING electrical. If the temp gauge moves at all, grounds.. :D