Hello,

Just signed up on your site, I have a 84 6.9 stock IDI just bought it about 3 months ago and it is my first diesel to own. The truck does not warm up, after I start it and it idles for a while it never warms up to normal temp. but when I take it out and drive it and run it up a hill it will warm up a lot like it is almost overheating and then when you slow down and get the rpms back down it will cool back down way below normal, what I am wondering is if the thermostat is stuck open or if it even has one. Or does it sound like a problem somewhere else? Any help would be great thanks. (I do plan on putting a new thermostat in it in couple of days)

 

yeah sounds like a thremostat for sure...

On the idling to warm the truck up thing, yes it is good to let it run for a minute or so to let oil get moving, especially in the winter, but they wont warm up like a gas engine will by just idling...your best bet is to let it run for a few and then drive it easy to get her warmed up before you flog the dog so to speak

 

if you are going by the factory "normal" gauge, don t belive it. go get a mechanical gauge. the factory gauges never work correctally.

but also it does sound like thermostat is stuck open. also when thermostat housing is off, make sure it still has the little plastic ball in one hole. you will see it right away.

and as for thermostats, make sure it is a ford or international part. many have had issues with aftermarket ones that like to stay closed or stay open.

 

I have already had to replace the guage and sending unit. when I got the truck it did not work at all. What is the best mechanical guage to get? So should I go to the International truck shop to get one, I have looked online at autozone and they show 2 different kinds, one kit that comes with 2 thermostats? Are these similiar to a gas engine or are they different?

 

go to ford or IH to get the thermostat trust me, you will be thankfull. the stant ones and other aftermarket one stick.

as for temp gauges, get any that are mechanical, and route the thermocoupler away from any high engine heat(manifold) to lower false temp readings. autometer, or even the cheap gauges from autozone pepboys ect...

your truck only has 1 thermostat, it is located on the passengerside of the engine, sorta next to/ behind the alternator. you will have to remove alternator to replace.

this is out of the Ford manual for the 6.9/7.3 idi engines
"CAUTION:Replacement thermostats other than the specified Motorcraft, or International Harvester thermostats may result in engine overheat damage. The specified thermostat does not contain an internal bypass, since the by-pass is located in the cylinder block. Therefore, whenever the thermostat is replaced, it is mandatory that only Motorcraft E5TZ-8575-C or International Harvester 1807945-C1 thermostat be installed