View Full Version : Cooling System Issues

11-22-2014, 09:22 PM
I have a problem with my ST - 1992 4AFE manual transmission car with 264K miles.

I recently went through some overheating issues and finally figured out that the problem was my rad fan switch. This happened in the summer and the problem was not so readily apparent as the engine would not overheat when the AC was on. Finally figured out (with big help from BGB) that if AC is on - the rad fan is controlled from different relays. So I just disconnected the fan from the switch and all was well for the rest of the summer.

Fast forward to now - I bought a few rad fan switch and installed it. In the process I drained the rad by pulling the lower hose, and then refilled with a gallon of anti-freeze topped off with water.

Now it seems the car never gets out of fast idle - and the heater blows cold even when the temp gauge is normal and the rad fan seems to be acting normal (off and then on after running awhile).

So - WTF?


Forgot to mention that I did change the thermostat and gasket last summer.

11-23-2014, 01:12 AM
Maybe you just need to belch the system a bit. They say Toyotas are notorious for that. when you fill it up you must have the heat control valve all the way open(set to hot) and it is even better if you park it so the nose is slightly uphill and let it idle for a little while with the cap off, you'll see the air bubbles coming out. It should automatically bleed itself after a few days of operation, assuming the vacuum release valve on your radiator cap works properly. But if you didn't bleed it very well in the first place you may have too much air trapped up in the heater core area.

This is assuming you didn't have some really dirty old coolant in there and it gunked up the heater core. If you still cant get it warm then you may need to drain it again and flush the hose that goes into the firewall where the heater core is.

11-23-2014, 01:41 AM
Hey Jacob. Try jacking the front up and running it. That sometimes helps to get the air out of the system. When I changed the radiator in mine this spring it took several tries to get all of the air out. I don't know what it is about them but it is difficult to get it all out.

11-23-2014, 03:44 PM
Thanks for the tips - as my driveway is the "Mt. Everest of NC" getting the front tilted up is no problem.

The cooling system had been pretty nasty originally, but has been clean since I replaced the rad a few years back. The heater worked fine before the fluid change so hopefully it's just an air pocket.

11-24-2014, 01:43 AM
Its likely an air pocket. Run the engine with the radiator cap off (do this from cold, put a funnel in it and put some coolant in the funnel so you wont suck air in), turn hvac control to hot, turn blower on full blast, let engine start warming up, and squeeze all the various lines in the engine bay, it will bleed it.

Once you stop getting air bubbles out by squeezing the lines, then put the cap back on, let it come up to temp and see if you have heater.

11-24-2014, 12:09 PM
In agreement on burping the system. And beyond what Luni said, tip that nose up, let it run with the funnel, let it get warm. Once you have a bit of heater put the rad cap back on. Then you can also try and make it hotter by holding the throttle open for a little while (5ish mins), then let it idle back down to a cooler state. The idea is to put some pressure on the system and move as much around as possible both parts wise (t-stat) and coolant flow wise.