overheating

[gxser]

hi i have a 96 4cyl dohc , and have an issue that i hope someone can give me a pointer with. when i start the car let it hidle for a while about 30 min it starts to overheat and i changed the coolant .thermostat,and made the coolant burpp and still have the same probleme . but whenever i take it for a spin it cools down to normal i dont have a clue whats the probleme maybe my water pump or head gasket ? please help me someone thanks

[umcamara]

Sounds like your rad fan might not be operating properly

[gxser]

ya it wasent working so changed sensor and all still nothing but got a relay switch and fixed the probleme but still i have a 92 4cyl sohc and let that car hidle for like 2h and fan dont work on it and tempeture gauge did not even nudge makes me wonder lol

[Inodoro Pereyra]

The SOHC seems to have what a call an overcooling issue. I had one, and even here in Miami, the fan never turned on, and the car never overheated. One day I had to make a "little trip", from Miami to N Virginia, and as soon as the temperature started going down, I had to start putting cardboard pieces in front of the radiator to keep the engine temperature within range. When I crossed into N Carolina, the whole radiator was covered in cardboard.

[umcamara]

The SOHC seems to have what a call an overcooling issue. I had one, and even here in Miami, the fan never turned on, and the car never overheated. One day I had to make a "little trip", from Miami to N Virginia, and as soon as the temperature started going down, I had to start putting cardboard pieces in front of the radiator to keep the engine temperature within range. When I crossed into N Carolina, the whole radiator was covered in cardboard.

I'd tend to agree. Although I'd add the DOHC to that list as well. I don't think my fan ever comes on.

[gxser]

thats od i live in alberta its -30 here and let my car hidle in the driveway lots of cool air circulating around the car but still overheats after 30 min on hidle i flick my fan switch on and she cools down right away or take it for a spin i just dont understand why it runs so hot on hidle i wonder if i should change my water pump i try to stay away from shops rather do the work on it myself and ask for info on this site thanks guyes

[umcamara]

Not sure. To me the engine SHOULD overheat without the fan on or the car moving at a certain speed. I wouldn't worry about it, seems to me like the car is operating the way it should.

I think us with the non-heating, non-coming-on-fans are the weirdos with weirdo cars.

[Inodoro Pereyra]

I would do a radiator flush. Maybe your car is overheating because the coolant flow is restricted.
Other than that, I agree with Umcamara. Normally a car should overheat under those conditions.

[gxser]

yea thats what i figured aslong it dont do it while im driving !! but funny thing is my sohc me and my friends tried to blow up the engine reving it to the tits i had 1/2 tank of gas .didnt overheat and fan didnt work aswell ran out of gas before anything happened just thought my dohc should be the same i guess ill just keep an eye on that thanks

[Ryan]

My mechanic did the same thing as you. The only thing that killed it was a brick on the gas pedal, no coolant, and a bag of silica sand in the valve cover. It ran until it was out of gas, and then never started again.

[Tunes67]

When your at idle and the car is beginning to overheat.. is your heater blowing hot at full heat setting? Or is it just luke warm? If your only getting luke warm heat from it while the temp is rising.. then its a sign that the water pump impeller is corroding away and is not moving the coolant as it should be. This is fairly rare, but I have seen it happen on an MX-3 DOHC RS. When the pump was removed.. the impeller was just a disc.. no fins or anything left to move the coolant around. As your engine RPMS rise the pump is spinning faster and can be a bit more effective since the uneven impeller causes a form of cavitation that does seem to move the coolant around more. So the issue seems to be non-existent when the car is moving.

Tunes67

[trife86]

When your at idle and the car is beginning to overheat.. is your heater blowing hot at full heat setting? Or is it just luke warm? If your only getting luke warm heat from it while the temp is rising.. then its a sign that the water pump impeller is corroding away and is not moving the coolant as it should be. This is fairly rare, but I have seen it happen on an MX-3 DOHC RS. When the pump was removed.. the impeller was just a disc.. no fins or anything left to move the coolant around. As your engine RPMS rise the pump is spinning faster and can be a bit more effective since the uneven impeller causes a form of cavitation that does seem to move the coolant around more. So the issue seems to be non-existent when the car is moving.

Tunes67

Kinda intresting.. My car is fine, but latley its been about 20-30F outside and if i sit at idle for 10-15min the temp gauge starts to rise. All this while i have lukewarm heat at best. Engine doesnt act like its overheating, and when driving even for 2hour drives temp is nice and low. I have no idea why i have no heat, Only gets hot if i really rev it high / beat on it for a lil and even than it only lasts for a min or 2

[gxser]

yea , i get really good heat when it runs and tempeture is good when driving its just when im sitting on hidle thats where she goes nuts !!! but you where saying about hideling it goes weird when i apply brakes it goes from 1000rpm to 2000 every second or more ? any clue what is doing that

[Tunes67]

Thats probably a vacuum leak.. when your pressing on the brake its activating the brake booster which uses vacuum from the engine to power the brakes (in essence anyway) if you have a vacuum leak.. the engine has to work harder to maintain the same vacuum level so the idle jumps. (This is a very basic explanation.. I am sure someone else could put it into more scientific terms ) Check the hoses n check valves leading from the intake manifold to the brake booster. Look for cracks or worn seals.

Believe it of not.. another really common idle issue is simply a dirty Throttle Body. Removing and cleaning.. resetting the TPS sensor.. adjusting the idle air mixture screw.. etc.. all will effect idle speed. Your idle at 1000 is pretty high.. should be more like 700-800 if I recall. If you havent had the TB off.. source some gaskets from mazda and remove & clean it good. Get a bore brush (aka a bottle brush) to make sure you get the air bypass hole. I did a write up on how to do this.. should be in the 4cyl FAQ section. A lot of folks reuse their rubber seals inside the TB & IAC assembly.. but to ensure no leaks I would suggest new (cheap from mazda too). If you decide to do this.. dont touch the idle air mixture screw until after you have done the clean up job.. and then only as needed. It could be set correctly already and then you would have to reset it again after doing the clean up. Its really not that big of a job.. couple of hours if you have the right tools. Just be patient and thorough. Save the TPS for last. Its easier to do with the TB off the car of course.. but if you dont have to remove it at all.. thats best. If you leave it on as you clean.. ensure that you dont get any cleaner fluid (whichever you use.. I like brake/electrical cleaner) onto or inside the TPS sensor.

Hope this helps

Tunes67

[Tunes67]

I just looked at the writeup I did on the TB clean and reset.. looks like car domain dumped all of my pics. I will have to set them back up. I will need Moderator help to do so though since its in the FAQ section. I still have all the pics.. I just have to reset the links.

Tunes67