Strange Temp Readings?

[LCBC]

So my 85 BJ 60 has been reading some strange temps for a while now. I pressure tested the system a month ago and found that the water pump was leaking so i installed a new one from Toyota; while i was at it i installed a new thermostat (part # 90916-03103) and rad cap (13lb). I flushed the system, installed new coolant etc... After doing all that i am getting weird temp readings; temp rises to almost red then drops. There also seems to be a correlation with the heater; when i have the heater set to high the temp goes up and if its at cold it stays relatively constant. I am also loosing coolant from somewhere. I have check the hoses and there does not seem to be any coolant in the oil (want to rule out the head) and havent noticed any coolant under the truck. I have only seen some coolant at the bottom of the rad (on the tray). So im trying to figure out if its:
a) the heater core
b) the thermostat (should i switch to a 82 degree) or
c) the rad (coolant leaking out and evaporating)

Anyone have any suggestions?

 

[bender3581]

My bet would be-air in the system.

 

[kim]

My bet would be-air in the system.

X2

I have seen this a couple of times.

 

[David*BJ70]

Disconect the higher cooling systeme hose ... on the fire wall. The hose on the heater valve should do the job. That will the better way to let out the air.

The thermostat can make some variation on the coolant temperature for the first km.

 

[LCBC]

So whats the process for bleeding the system? Disconnect the higher hose (for how long? while the truck is running?) Its been like this for a couple of weeks, wouldn't the system have purged itself by now?

 

[bigboss]

the heater hoses because id say the the highest point how much coolent is being lost ,is ther a rear heater in that system these pipes rust and just mybey it could be suking air the in some strange way when the vehcle is off had this on a hino before brazed up the hose and the prob went away

 

[LCBC]

I removed the rear heater last year b/c it was leaking; the hoses to the rear heater have been conected with a coupling - no leaks. I have to top up the coolant once a week and the reservoir is always low. I can also smell coolant when the heater/fan is on. There are never any signs of coolant being lost on the ground so????

 

[bigboss]

hey lcbc i just had a look at a picture of an engine same as yours and there is two pipes to the heater that run above the exhaust do you think maybe these leak when exhaust heats them up an at the same time leak on to the manifold and hens the smell but also no leak on the ground because it will burn away i dont think a presure test will find this because it may only be seeping out under temp and pressure ,, just a thought hey