blacklite

This one doesnt make a lot of sense to me. After 2 weeks of searching forum, I decided to post.

My 91 rx7 NA overheats once the AC is off and particularly when idling. As soon as the needle starts to move past halfway, I can turn on AC an it heads back down.

I have the fan duct and plastic undertray.
I replaced the thermostat straight from mazda w/ jiggle pin (previous owner removed it i guess..).
Radiator is a Calsonic with no apparent leaks (or anywhere on the system for that matter). I cleaned the sprung radiator cap - rubber was fine. When I drained and flushed the radiator with distilled water, the old fluid smelled kinda like gasoline and rust deposits came out of the flush. In addition, there are parts of the radiator that looks rust colored.

Currently investigating the fan clutch.

Any thoughts?

samjaza78

Fan clutch, potentially a loose belt- do you have an air pump or no?

I ask because, when there is no air pump belt, there's a tendency to slippage on the water pump and clutch fan. Your A/C clutch may be 'pulling' the assembly along.

blacklite

Yes I do have an air pump. I tested the fan clutch by spinning it some bit after it as it was cooling down - still had some resistance.

I am thinking maybe a water temp sensor is dead or else coolant seals, despite the absence of most other symptoms.

blacklite

So I tried turning it on again without AC to test the fan and then the temp gauge held halfway.

Drove down the street about a quarter mile and then the heat creeps to 5/8-3/4 on the temp gauge after pulling over ('Add Coolant' flickered on/off). Came back down after picking up speed to take it back home. Every slow down, the temperature creeped back up.

Evil_Sephiroth

iTrader: (1)

But when you turn on AC if I remember fan start to work.....

Probably this give more air to radiator....

gerald m

The thermo fan reacts to temp hitting the fins on the fan base , it is very possible that the extra heat created by the ac unit makes the fan clutch work to some degree when the ac is off there would be less heat created and less fan speed .. it is almost unheard of for a thermo fan to out last any vehicle .. the fan probably needs replacing anyway .. Might want to check the fan blades and make sure they are in good shape and not flexing to much to , a fan blade needs a nice pitch to move the air proper

When the engine is up to or past normal running temp that little fan should be really turning and you should be hearing all the extra air it is moving .even at 1000 RPM.s

A electronic temp gun would be handy to check temp in different areas of the cooling system .. JMO good luck

blacklite

Thanks Gerald, I have access to a lot of test equipment...perks of being a former Former SAE lead at CSUS.

Evil Seph, I thought the same too. I know it doesnt if I turn on the AC but not the engine, but then that kinda makes sense given that you need heat for an evap to work.

samjaza78

If the coolant light's started flashing, I'd pressure test and burp the system.

Creep could also mean your radiator's starting to deteriorate- which wouldn't be completely surprising, considering the condition of your coolant before the flush.

blacklite

Samjaza

While the radiator seems like **** to me, I'm preparing for a rebuild. I tried cold-starting with the radiator cap off. Coolant immediately flowed out of the filler neck until the engine simply stalled. I am confident that combustion gases have made it past the inner coolant seals and pressurized the coolant system. Having recently installed a new OEM Mazda thermostat, I know it should not be at fault. Block Coolant pressure is just driving the thermostat open.

Please correct me if my logic is off as it would save me $$$. Normally I am one for full tests with combustion and coolant pressure tests but I would say what happened is sufficient evidence.

blacklite

For the record and anyone searching threads:

I pulled the EGI and cranked after replacing some gaskets and hoses - coolant flowed out of the filler neck. Based on my research, that is indicative of combustion/intake/exhaust gases making its way into the coolant passages. After all, the coolant system is a closed system with respect the rest of the engine. When buying a 7, dont get too excited, do the proper tests and adjust your price accordingly. And be prepared for extensive repairs if the engine has be inactive for a number of years, ESPECIALLY if it was not stored for long periods of time as advised.