Hi, I've got a 1986 Toyota 4x4 with a heater problem. I've felt the heater hoses and one of them is definitely warmer than the other. The heater does blow some heat, but its very minimal. I think the heater core is probably blocked up, but the coolant temperature gauge never gets to operating temperature. Could this be the result of a stuck open thermostat? I think its probably an issue with the temperature gauge or coolant temp sender and heater core, but I don't want to go through the work of tearing out the heater core if it could be an easier fix. The truck runs great other than this, any advice is greatly appreciated, thanks!

 

Pull your thermostat and boil it in some water on the stove to check for function. If you have a thermometer you can stick in the water, use that to make sure the thermostat is opening at the right temperature. Just remember don't let it sit on the metal bottom of the stove. The metal will transfer the heat directly to the metal on the thermostat and give you an inaccurate reading. Suspend it with a string or set it on a plastic something-or-other on the bottom.

It sounds like you have a problem with your heater core. You'll have to look into that.

 

Was any stop leak ever used?

 

Check to see if the heater valve on the firewall is functioning properly.

 

I have the same issue but my my heater works perfectly fine and the temp gauge is about 1/4 way up when running normal.

 

I've had 2 Toyota trucks (84 pickup and my current 86 4Runner) that the dash gauges on both never read correctly. I replaced all 3 coolant sensors on both trucks but the gauge would jump from all the way down to over heating in a flash. If it registering half way up after about 5 minuets warm up hen its operating fine, but should not just jump up there.

If your thermostat is stuck open or missing all together your engine either run very hot or never warm up depending on your radiator...

 

Thanks everyone for the responses, the radiator hoses definitely get warm, but the coolant gauge doesn't rise at all. (should've clarified that in the post) I recently bought the truck, so I have no idea if stop-leak was every used in the coolant. I'm gonna try and work on it a little today, if the coolant gauge doesn't rise at all, even if I drive it for an hour, it must be the gauge or the sender right?