ok im having some issues. my car is overheating on the highway. i did a coolant flush installed aftermarket temp gauge with the oem gauge still working, new mazda thermostat, aluminum thermostat cover, new hoses a few weeks ago. the stock gauge sender broke so i replaced it with an autozone one yesterday. drove the first time with the autozone sender on the stock gauge today and it started to climb. i saw temps of 210 on aftermarket gauge and pulled over immediately to cool down. thought it was air in the system which there was some so i burped it back to normal. it cooled down on the street but gets hot on the highway. i have all the plastics like the undertray on. im gonna get a new rad anyway but until then i need some help. its fine on the streets now but the highway it climbs. i pushed it shifting at 5500 rpm for a little bit 1st, 2nd,3rd,4th gear after burping it and the stock gauge stayed at the center but the second i get on the highway it starts to climb. i know the stock gauge isn't too accurate but mine still works as fine as it can and i take it into consideration. i'm thinking the autozone sender is **** or my rad is busted but i see no leaks. all this started happening after i put the autozone sender so i suspect its that but i'm not 100% certain it sucks and that the autozone is correct and the old stock one was crap after being in there for 22 years. any help is greatly appreciated. no smoke or anything like that so im sure its the rad system

 

Your car is acting backwards and I doubt the sending unit is the cause, it's something more fundamental.
Highway driving is the absolute least stressful environment for the engine to be in...nice, high pressure forced air into the nose and relatively low, steady state rpms (in 5th mine runs 2900 rpms at an indicated 80mph).
And yet, you overheat.

What fan setup and what rad are you using?
I'd suspect the radiator first.

 

Stock rad and clutch fan.

 

AC?

If you've never done so (and have AC), cleaning the radiator might do it.
The exterior, not the inside.

When I first pulled my car apart the space between the rad and AC condenser(?) was jammed with leaves and other organic gunk...half the radiator was obstructed. A bit of high pressure hose work solved the problem.
It's easy enough to check.

 

Yeah I have ac it just needs to be recharged so I never even turn the thing on. I did vacuum the rad after I flushed it before I refilled the coolant. And it was all working fine up until yesterday. I have my auto mechanics class today so ill lift the car for a better view and check rhings out again. Could the rad cap cause these type of problems?

 

I think IIRC you can get to the space between the radiator and AC condenser by removing the overflow and the plastic pieces between the nose and the cross member. As clokker said make sure that is all clear. Mine runs it's coolest on the highway.

 

Did you replace the cap? If the cap is bad it will burp out water and you'll get an air bubble in the system, causing what you describe.

 

Why then would it only happen at speed?
Seems like air in the system would cause problems at idle as well.

 

I notice it only does it in 5th gear with consistant rpm @3k and up. I stayed consistant at 3k in the other gears and it only does it in 5th. The cap does need to be changed. Ill pick one up today

 

It started overheating on the street as a well now. The stock gauge skyrocketed near H. the aftermarket showed around 220 I stopped immediately and turned the car off. Could it really be something simple like the cap? I just got hired at a mazda dealer so if it is possibly the stupid cap I will buy one right now since im here if they have one in stock. The other dealer I usually get my oem stuff at has them in stock but im nowhere near it :\

 

Are you getting extra water in your overflow tank? If so, it is the cap. If not and you are low on coolant you have a leak.

Worst case it could be a bad coolant seal.

 

Clearly the OPs situation is deteriorating.

Sometimes at idle there is enough flow even with an air bubble to keep things happy.

As you indicated, if you have a problem with temp at speed, it is usually a flow problem with water or air.

 

mine does the same thing.... still cant figure it out. replaced water pump, thermostat, radiator, burped system. It will be fine on street driving, even with high ambient temps. but as i get on the highway, temp starts to climb and holds steady at about the half way mark on the stock s4 gauge.

 

Have the undertray installed? You didnt mention radiator cap.. did you change it?

 

ok i talked with will (i think his name was will) of lucky 7 racing and explained my symptoms. he said it could be clogged since its an old radiator and likely has some gunk inside or a leak possibly i might take it in to get it checked out if i don't get the new radiator soon enough.

 

Your fan clutch is bad. Replace the fan clutch and you will be golden. Had the same exact experience on an S4 NA a couple of years ago.

BTW, an S5 fan clutch will fit both the S4 and S5; the S4 fan clutch will not fit the S5.

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We matched your request.


Year
Part
Model Description Part
Grade Stock# US
Price Dealer Info
1991
Fan Clutch
Mazda RX7 e1764 PRX10336 $40 Mazda-Nissan Heaven USA-TX(Ft.-Worth) Request_Quote 817-572-0277 / 817-563-2277 Request_Insurance_Quote





Call Mario. Good guy, knows his stuff. This is no pick n pull type outfit.

 

Very possibly true, given the price I doubt many were replaced and they're getting old now. BUT...

The issue first manifested on the highway, where no fan at all is usually necessary (and in fact, is an impediment) and OP claimed it would idle just fine. Idle is a worst case scenario and I'd think a bad thermoclutch would be obvious in those conditions, yet it appeared to work OK.

The fan clutch could very well be dying but my money is still on the radiator.

 

My experience with dead fan clutches is they tend to lock or not want to free rotate. The extra driving force when not necessary can produce weird problems. Over heating at speed? I don't know. Usually one can hear the fan working over load when the clutch fails and mileage gets even worse.

 

i read a thread about the clutches for the fan and it said to spin it by hand and if it stops with friction then its good if it spins freely then its bad which mine doesn't spin freely at all. unless that was untrue or i have it backwards.
i still am thinking its the rad. actually it first started on the street while driving. then i got home burped the car of air which there was a good amount and all was fine until i got on the highway later that day. i got off the highway and let it cool did a bit more burping at a gas station and it was fine for a while on the street. there is this long back street where i was doing freeway speeds(60 mph) and testing and only at freeway speeds it was heating up under a consistent 3k rpm. i was taking off normally gaining freeway speeds under normal conditions without excessive revving and whatnot . i let it cool again and drove normally on the streets and it was fine now today it started heating again but on the street even more than yesterday. now it was 90 degrees today so i think that contributed to todays mishap.it was mid 70's yesterday when all this started. i bought a new oem rad cap and it didnt help but it was only 20 bucks so oh well LOL do you think the thermostat may be faulty? its an OEM mazda thermostat i bought brand new. do you think it could just be a bad one? i mean it all was fine for weeks after the install could it be acting up now? ill look in to the fan clutch for sure. even if i buy it and don't need it it'll just end up for sale here to help someone else.

 

I overlooked where you said stock radiator...

As I always say, if the plastic caps on the rad look like the backside of your rear view mirror, replace that ****.

I bet you are getting air in the system from a tiny crack in the plastic tank and I am also willing to bet that tiny crack is near the upper radiator hose connection.

 

Yes stock rad. Ill be picking up a koyo in a few days

 

I have seen a water pump cause the same issue. At lower rpm it works fine but at higher rpm worn pump impellers cause cavitation and the coolant doesn't flow.

 

Possible. once I get the new rad ill change it out just in case

 

New radiator and cap, no external leaks, new thermostat, new water pump, Burped system. Electric fans. Even with the fans on on the highway temp rises and steadies at 1/2 mark. Then lowers to 1/4 mark on city driving.

 

Dont think fans should be on on the highway