Mazda Protege '91 overheating

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My '91 Mazda Protege (DOHC) recently started giving signs of overheating.

While driving at low speed (engine RPM rather) or even idling, from time to time (NOT always) the temperature gauge starts to quickly creep up. If I speed up - basically rev the engine above 2500RPM the temperature gauge quickly comes back to normal. On long driving at highway speeds (for this car in fifth gear it is 3500RMP at 70MPH) everything works flawlessly - the temperature is perfectly stable at just a bit below 1/2 scale.

Here is what I tried in order to diagnose the problem:

1. The engine idle is OK - 1500RPM when cold then slowly coming down to 740 and stabilizing.
2. When the engine warms up the thermostat seems to open up - the top (thick) radiator hose becomes warm.
3. The fan turns on when the car is not moving and has warmed up enough.
4. The heater in the cabin blows warm air when the temperature is normal and COLD air when the engine starts to overheat.
5. The same goes for the radiator - if I just idle the car and the engine starts to overheat it warms up a bit (starting from the top hose) but not enough at all. If I rev up the RPMs the engine temperature drops and the radiator becomes hot.
6. I was afraid I could have blown a head gasket because of the overheating (even though I never rally hit the "top"), but there are no bubbles or oil in the coolant, no traces of water in the oil and no white smoke from the exhaust.

So here is what I did:

When I bought the car (140000mi) I immediately noticed that both the alternator/water pump and the power steering/AC belts were in bad condition. The former one in particular (a V belt) was glazed and would squeak from time to time. I never found the time to change them though.
With the above points in mind and having read all of the threads about overheating in this forum my first guess was that the belt eventually got too loose and did not turn the water pump efficiently any more. So last weekend I replaced both belts.

Unfortunately the problem remained exactly as before. I am a bit uncertain whether I have tightened the belts enough - the guideline in the Haynes manual was fuzzy at best "0.32 to 0.35 inch deflection with moderate pressure (22lb) for new belts" - well I am not at all sure that I can properly judge 22lb. And moderate does not really say anything.

So now I am at a loss. Any suggestions as to why the car is overheating and how to properly adjust the belt tension will be truly appreciated.

Thanks in advance,

P.S. This message turned out quite long - I apologize and thanks for the patience

posted by  ruevs

Item 1 is normal for most cars especially during cold weather.
Item 2 is what I would expect
Item 3 means the cooling fan circuit is working
Items 4 and 5 are not normal
Item 6 - if the car is running OK except for overheating, your head gasket is probably OK

these are my two guesses

Check the water pump belt tension. If belt tension is OK then pinch the radiator hose after the engine warms up enough to open the thermostat. Let it loose. If you don't feel a pretty healthy surge, the water pump is kaput and needs to be replaced.

posted by  tbaxleyjr

>pinch the radiator hose after the engine warms
>up enough to open the thermostat. Let it loose.
>If you don't feel a pretty healthy surge, the
>water pump is kaput and needs to be replaced.

I did not use the car today (bicycle) but I will check in the evening and post my findings.

As for replacing the water pump - is it a one man outside on the parking lot king of job? From what I saw I'll need to remove the water pump and AC belts, the crankshaft pulley, the timing belt covers, the timing belt itself... maybe more? The space between the "front" of the engine and the side of the car seems awfully tight... And flush the whole colling system in the end.

posted by  ruevs

One more thought - why does it not happen always. I.e. if the water pump was bad it should fail to pump enough water at low RPM all the time. Or am I mistaken?

posted by  ruevs

possibly - the reason to do the check with the car @ idle.

The cooling fan may be running but too slow

If the car has AC, and the AC or defogger is on, many cars have a second cooling fan which may not be coming on

A third another cause if the ignition timing may be off spec.

posted by  tbaxleyjr

From what you've told us so far, your car hasn't actually overheated yet, you say that the temp guage quickly rises but you dont say to how high. If the car does overheat and lose all or most of its water, your heater wont work (Ref. item 4). I could do with a little more info, and if it hasn't yet overheated your head gasket will be fine. That's not to say tbaxle is wrong of course, I just feel the need to ask for more info :thumbs:

posted by  Cliffy

Cliffy - Good point on checking coolant level first.

If the level is low, no coolant in the overflow bottle and there are air bubbles in the system, the temperature gage will swing like reuvs is describing. If this is the case, the first thing to do would be open the radiator cap, make sure the radiator core is covered then top off the coolant recovery bottle to a little above full hot (although the car is cold.) The system, after being driven a time or two, will "burp" the air bubble and the level in the overflow bottle will go back closer to where is is supposed to be.

I sometimes overlook simple stuff. I have fooled around with cars but also know I am not God either.

posted by  tbaxleyjr

Hi guys,

Thanks a lot for the suggestions.

1. I checked the belt tension - seems a bit loose (definitely looser than when I installed it). Might have loosened either because the bolts were not tight enough or just after running a bit. But the belt definitely still turns both the alternator and water pump - even at idle - it may be slipping a bit though - no way to tell. After Easter I will spend the time to tighten it. I need the car this weekend and no time to do it.

2. I did the "pinch the hose" test. The hose definitely feels more "pumped up" when I rev the engine compared to idle. And one can even tell by touching the radiator next to the hose - it is on the cool side when the engine is idling (and staring to overheat) and gets hot as soon as the RPM's go up (engine cools down of course :-).

3. The coolant level was the first thing I checked - it was at low when cool and the first thing I did was added 50/50 mixture to the full mark. If I open the radiator cap the fluid is to the edge - even overflows a bit if I start and rev up the engine. This did not help with the "overheating".

4. The fan runs like a tornado - I would not like my fingers or anything at all to get in there when it is spinning.

5. As for how hot the car gets - it never actually hits the top of the gauge. The normal temperature is just a bit below 1/2 and gathering some courage I left it to idle for some time, while watching the gauge, It went up to maybe 4/5 but never above that. Unfortunately I do not have a suitable thermometer which I can use to measure the exact temperature. But it gets very, very hot to the touch - perceptibly hotter than normal. I actually did a (call it stupid :-) test - I spit on the engine next to the spark plugs - my spit at least did not boil, but it evaporates VERY fast :-) Do not laugh at me too much for this... in fact you can laugh - it is funny :-)

So this is all the info so far. As soon as I tighten the belt I will post an update.

posted by  ruevs

Sounds like a bad water pump to me.

posted by  Sonreir

If coolant level and belt tension does not fix problem then I am sorry to give an opinion the waterpump is kaput.

I understand your pain upon hearing this kind of news. I put in a new water pump in a Mazda 626 my daughter used to own at the same time I changed the timing belt. I did not want to go through the pain of tearing the front part of that car down again to get to the freaking thing a few thousand miles later when the waterpump wore out

posted by  tbaxleyjr


I know that this thread is old, but how did you make out?

I have the same problem on my 92 protege dx.

Please email me at if you have the fix for this. (as I probably will not be able to come back on here to check any responses)


posted by  92dxbeater

I owned a 91' protege and had this same problem. The way I found out that my w/p went out was loosening the alt belt and grab ahold of the w/p pulley and try and move it.(up/down) If there is alot of play then the pumps prolly bad.Also (with the belt off) give the pulley a good spin. If it spins freely without much resitance it's also a sign of w/p failure.

And to replace it it took a good four hours out of my day off.(3 hrs to do another hr to reset my timing DOHC+ADJ Cam gears= :banghead:

Not to mention the entire left side of the engine bay must come apart.

posted by  pnj4l


Even more time has passed since you psted this but here is an answer anyway:
After I tighthtnened the belt the problem went away (that was in Ocrtober 2004).
Last month the same thing happened again - only once - time to check the belt tention again I guess...

posted by  ruevs

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