jmseven

Yesterday on my way home to Sacramento from San Jose (150+mile trip), my temp gauge started to rise @ aprox 6000 rpm @80mph, going up the steep hill on hwy 80 @ Vallejo. Outside temps prob over 85 degress F.

I immediately turned on the heater and the temps dropped. As soon as I hit the valley, I shut off the heater and did some 4th gear runs @ full throttle...again, the temps seem to rise. Once off the load, crusing @ 80mph, the temps stayed steddy.

I did chk the fan clutch and it does have resistance but not alot. I can move it back and forth pretty easily...but, why is the temps steddy @ speed? I chkd the water level. It is leveled. I have all factory new parts, cap, thermo, upgraded radiator.

Can this also be cavitation?

Silkworm

What RPM? How old of a water pump?

Temps without load will be down due to airflow through the radiator, just from cruising. This is why I can get away with not having a fan at all.

High RPMs, low speed (like a hill), and yeah, you can have trouble. When did you last flush your radiator and coolant? The radiator could just be gummed up, time for a new core.

HTH

PaulC

jmseven

RPMs: just about 5500 to redline
Waterpump: Unknown
Radiator: upgrade, cleaned and flow tested prior to engine install
Coolant: still fresh.

When I installed my new engine, I chked the pump. It was perfectly fine..no play, no give, no leaks.

That install was 14k miles ago. I had already changed coolant twice, both w/ Redline Water wetter (thank god, I think that is what saved my engine).

I believe that I did have cavitation. My belts were looser yesterday..maybe due to the F'IN hot *** weather. Plus, my fan clutch is bad...going to replace it tomorrow.

'Vert in Vegas

Is it possible you are low on oil?
Going up a grade could definitely create higher temps which would be MUCH more noticeable when low on oil.

jmseven

Vert in V...

You know that was something I did not think about. But, I did chk my oil prior to the drive to Sac. Funny you mentioned that, because I had added 1/4 of cheap oil ,10/40, to get it past half. And, I only use 10/30.

Just chkd, I now have 1/3 from low left.

What I will do is chg the fan clutch, alternator belt, and an oil chng.

I am closer to solving this. I believe it was cavitation.

tims

At 6000 rpm the water pump will not cavitate unless you have air trapped in the system. I race my turbo II as well as two other N/A 13b's and run them continuously for hours at a time over 8000 rpm and have never had any cavitation or overheating problems that were not caused by other issues. I have raced my car at temps over 120* F outside with no problems. the main problem with the second gen cooling system is that the radiator is lower than the engine. this is why there is a rad cap on the top of the water outlet. this means it is absolutely mandatory to bleed the air out of the cooling system and to flush the radiator regularly. also the stock radiator is very small and at high loads(uphill at 80mph) and high ambiant temperatures the water temp is going to rise. this is why when you turned on the heater the temp went down. if the pump was cavitating the heater would have done nothing. your situation does not sound abnormal. I would check or replace the fan clutch as this sounds like your problem. also do a pressure test to make sure there are no other small leaks that could be unknown

'Vert in Vegas

I just found a very small leak where my radiator filler is bolted to my radiator. It was drawing air into the system during cooldown.
The STEALER doesn't have the gasket, and ordered one for me for $4. (@#%@**)
I found a O-Ring at PepBoys that works great.

jmseven

I picked up my fan clutch @ Mazda recycling. They gave it for $35 PLUS a SIX month warranty! I didn't mention it, but everyone was asking for $45 for just the clutch. Also, install new fan belts again.

It seem to work. I warmed up the car completely. I did 4 sprints to redline and the needle did not move. How MUCH resistance should the clutch actaully have? I could not find any specific DETAILS on that subject.

You know I should mention that my stock temp gauge reads half ALL the time. I used the previous temp sensor from the original block. That block overheated and caused major problems (bought it that way). I believe that the sensor was affected.

Anyone?

'Vert in Vegas

Half-way on the temp gauge is the correct reading.
The fan clutch shoud spin easily about 1/2 to 1 turn - no more- when cold.
When hot it should take a lot more effort.

Fingers

sometimes my temp goes past 1/2... almost to 2/3rds ... usually when i'm crusing at 3500RPM on the highway. Why?! New engine, new coolant, all fluids topped, fan clutch seems good. (hard to spin when hot, doesnt go past 1/4 turn when cold) What's going on?

'Vert in Vegas

Try this;
Check your oil cooler and see if the fins are clogged.

ponykiller

Last week I changed the oil on my 91 vert, and while I was under the car, I pulled off the black plastic underbody and saw alot of leaves/junk trapped up by the radiator. I have never had any overheating problems, but I could see the leaves trapped above the black plastic underbody and I wanted to be sure that I never do have any problems.

I saw a lot of leaves trapped between the A/C radiator and the coolant radiator. There is a metal piece attatched to the bottom of the A/C radiator that is supposed to guide the air to the radiator, but I found that it was trapping lots of leaves. I took a screwdriver and bent it out a little bit to allow all the leaves to fall out.

Try cleaning that out, and see if your temps drop.



Kris

jmseven

@ 14K miles ago, I did remove the radiator and oil cooler, when I sent them out for cleaning. There were some leaves, but not alot.

I couldn't have THAT many leaves. I dont park ANYWHERE that leave would accumulate....trust me, I am a city person...NO TREES.

But, I just got back from the gas station. I started to hear the dreaded waterpump whine. It was NOT loud, just a small whisper. I will be changing it next week. I hope.

The Ace

Man, I had the exact same problem Saturday. VERY hot outside, just cruising to get to my g/f house, and when I stop to pick her up, the temp gauge starts to rise

I immediately start to cruise around the block, the temps drop. As soon as I stop, the temp goes up again. I shut off the engine, check the engine bay, fan is not working at all No coolant overflow, just the fan is not working...I leave the car there and we drive in my g/f car to get to the beach

When we get back, I check the Rex, coolant has returned to radiator (this is a problem I've been having for like EVER ) Anyway, I start up the car, fan is now working fine I have agreed with my g/f that I would just drop it off in the Mazda shop, so we drive over there, and on the way there, NO problem at all (it was already afternoon though, so the outside temps were way lower). Check the car again, coolant is fine, fan is working, belts are all there nice and tight

Car has just had its 100K service-tuneup, radiator flushed, new plugs, oil, coolant, fluids, belts, filters, everything. No audible sounds from engine bay, fan is working nicely, all seem in order....

Anyone has ANY ideas about this ?

Scott 89t2

the fan doesn't mater once you are moving. I'll say the problem is something else.

is your airpump on? if not I'd say belt sliping.

The Ace

Yeah, but you see, when I was moving the temps would drop, and when I stopped the temps would rise. Then I check the fan (because thats a dead-on giveaway for a faulty fan), and its not working, so I say "there goes my fan". But when I come back, and start the car again, fan is working just fine

Airpump is still on, working cats, no squeeking from engine's belts (so no slipping), shrouds are all intact

Anyway the car is in the shop, so I guess I'll know pretty soon. I thought maybe they put in a cheap thermostat, and it got stuck

SureShot

The fan clutch will slowly start slipping as it ages. On your series 5 the fan should pull really hard up to about 4K when the motor is hot. It should maintain about 4K as the motor revs higher. (I wish someone would come up with a supercharger drive that worked the same way.)
Sometimes you can get more life from it by bending outward the bi-metal strip on the front of the fan clutch.
Also check where the valve disc on the bottom of the thermostat seats in the water pump housing. That bypass is only supposed to open at high revs..
Bill.

The Ace

Well, guys at the shop say everything works fine and as expected Just changed the thermostat (another 50 EUR ) so everything is brand new....

Fan clutch is also fine, and fan rpms are as high as they should be. Car doesnt overheat, it just did that one time (and I think it ALMOST did another time). Guess I'll just have to wait and see....*cross fingers*

akageals

Fingers....I have the same problem on my '87 TII. Fine around town but on the interstate it gets hot. Let us know what you find out.

Todd

SureShot

The s4 fan clutch is more linear in how it bites. Hotter air on the bimetal = more bite. The s5 clutch is more on/off. Bending out the bimetal will compensate for wear - up to a point. If that fails to cool, you can get a new fan clutch or convert to an electric fan.

Scott 89t2

sorry my reply was for the top post which was heating while moving

The Ace

So any one of you guys knows exactly how the cooling system turns on the fan, and with what mechanism ? I have the FSM right in front of me, and the only thing that it says is that:

Overheating could be caused by bad thermostat, clogged fins, insufficient coolant, loose belt, thermo-modulated fan failure (but what exactly ??), electric fan/relay failure.

But how exactly is the thermo-modulated fan activated ?

jmseven

I found the problem!!!

I had just completed a pressure test. I do have a leak. It is the hose that runs from the throttle body (13-6800-N350) to the rear housing.....

It only presure tested to 10lbs. It bleed off REALLY slow. I will be driving it back home VERY late tonight when it is cooler...right now it should it 100 degrees in the valley...ouch!

If you having UNKNOWN cooling probs...this might be the actual problem.

The Ace

I have already replaced this hose..... and others as well......





...........and STILL I have this ******* problem

jmseven

It is possible that your thermostat did stick.....then opened....it might of been just one of those days.