I'm helping a friend out to get his 1st gen back on the road. It sat for a year. The stock gauge in the dash cluster shows that after a good 5 min or so the engine coolant temp rises to near the top / hot so I immediatly shut her down. So far I've changed the thermostat to a original Mazda one and ordered him a brand new Aluminum radiator, both which have not solved the problem. It also has a brand new waterpump that he installed prior to me messing w it and it seems to be installed correctly. Also it has a electric fan. I found the original fan in my parts stash and going to give that whirl tommorow. Any other ideas...?? I'm really hoping its not the motor. When he bought the car from the previous owner there was a full master rebuild kit for the 12A included. Ohhh, its a 83 model w/a two barrel Holley. Thanks.

 

I would install an aftermarket gauge (even if temporary) and see what it reads.

 

Try putting a box fan in front of the car when it idles. If it runs normal with that then it must be the efan not pulling enough air.

Does it have AC? try power washing the condenser or remove it if you feel you can. At least you dont live in the south! No AC in NY shouldnt be too bad.

 

Somewhere deep in the memory Rolodex I recall bad coolant seals leaking compression into the coolant causing overheat situation...? How do you check for something like this...?? Besides swapping motors...???

 

So I put the stock fan on today. It pulls ALOT more air then the junky e-fan he had on there.

The stock temp gauge still climbs to hot just a little slower. I'm going to try putting on the shroud and under tray, however my car has had neither on for the past 5 years and doesn't see over 1/4 on the temp gauge EVER.

Maybe I'll try a new temp sensor...??

 

Other than replacing the entire cooling system have you tried adjusting idle mixture and timing? That can cause over heating. So can a clogged exhaust. A bad coolant seal will cause over heating due to exhaust gas being forced into the radiator, but it is not common on 12as. Mainly s4-s6 13bs if I remember right. The infamous champagne test. Your level would drop every drive, your coolant buzzer would come on every drive, and your overflow tank would boil out onto the pavement if it was the case. Although it is easier to just sniff the coolant. Pour some out into a clean water jug and smell it. If it smells like exhaust than thats your problem.

 

Awesome...! Thanks NCross.

 

Ehhhh not so awesome after all. Bc it wasn't showing the signs you mentioned above I thought that was a good thing. I took a compression tester to the motor and front is bouncing around at a 100, back is bouncing around at 60.

 

Rebuild! Low compression still shouldnt cause over heating.It must have over heated and warped something.

 

So I've been battling this overheating situation for the past two weeks as time permitted. I found a motor to swap out from a fellow rotorhead buddy, that didn't do the trick. Swapped out the two barrel Holley for a Dellorto, that didn't do it either. Swapped silly beehive oil cooler, sensor, dash cluster....

Somewhere in the middle of all this I added a aftermarket gauge at the thermostat neck and it read fine. I was scared the beehive area where the stock sender sits was overheating and didn't want to mess up the new motor. I was running out of things to try.

I gave giving the motor a good ground as close to the sensor as I could get, in a **** in the wind last ditch effort and could you believe it did the trick. Lolololooooo. The stock gauge now sits about 1/4 from the bottom, right near the "C" as it should.


Thank you Colin...!!

 

Anytime Jimmy...glad you got it sorted out.

 

Id like to see a picture of the ground if you dont mind. Curious as Ive encountered this before myself...

 

The thing I don't get is there is a giant ground strap from the negative on the battery to the starter/motor area.

NCross... It's nothing special. Just a 10awg wire from the block to the firewall. I should prob up the size just to be safe.