OK, guys what is up with my truck? When I pulled the thermostat out of it, it had a thermostat with a "tube" like end on it that, I believe, is supposed to close off the bypass as the thermostat opens. Correct??

I go to the Ford dealer and ask for a thermostat for a 91 IDI, they give me a regular thermostat. No tube on the end. The one for a 95 and up DI has a small plate attached to it that I believe would be to close off the bypass, but I am not sure the diameter of the thermostat is right (2.5 inches).

Which thermostat should I use, or how can I find the right one?

 

If you went to the dealer and stated the year of your truck they should give you the right one.The t-stat for these years do not have the by pass ,the by pass is built into the goose neck,its a little ball thats up inside the goose neck.Make sure the ball is free but do not remove it or you will have trouble.Only use the oem t-stat.

 

I do not believe my gooseneck has a check ball in it, but when you pull the thermostat out, looking down into the housing, there is a circular piece like what the thermostat would slide the tube into.

 

The round hole in the block is the bypass, the check ball is an air vent, do not remove it but ensure it is free moving, clean, the ball is round and rattles

How to get and check it.........

CAUTION:
The specified/required thermostat does not contain an internal bypass, since the bypass is located in the cylinder block. Whenever the thermostat is replaced, it is mandatory that only Motorcraft E5TZ-8575-C or Navistar 1807974C94 thermostat be installed.
CAUTION:
Do not attempt to repair any thermostat. It should be replaced if it is not operating properly.
Check the any new thermostat before installing it for correct opening temperature. Before suspending in boiling water, with a flashlight check where the rubber and the flat metal flange meet for bad seal. Tstat should start to opening barely at 180-192f, fully open 200-212f, allow to cool and check for rubber seal again.
Removal: Disconnect batteries, drain 4+ gals A/F, remove: as required, fan belt, alternator set aside, alt bracket, remove filter support from fuel filter then e/block. Disconnect upper rad hose at rad, remove tstat bolts and housing. Clean both faces, depression and holes in block, ensure check ball in goosekneck is clean, free and rattles "do not remove".
Installation is reverse proceedure, I do not use sealant on gaskets and faces. REMEMBER the tstat pellet(copper end) goes into the block. I do use a "very small amount" of sealant on the edge of the tstat face when installing into the recess, now go for coffee, allow sealant to setup, this has saved me from tstat slippage when the gasket and goosekneck are installed.
Manifold bolt torque......... 20ftlbs

 

Thanks Sooo much for the help. Quite apparently, someone before me installed the completely wrong thermostat. The local ford dealer does have the right one, it goes in this weekend.

 

what happens if you just take the t-stat out?

 

89ford73,

I REALLY wouldn't do that. Thats bad news on a gas engine, but will kill a diesel quick. Diesels need to be running at temp so that you get proper combustion.

You romp hard on a cold diesel and something will break.

 

Would a really long warm up duration mean that my thermostat isn't operating properly? It takes about 5-7min for that cold idle solenoid to kick off. I'm wondering if this has something to do with my thermostat...Any ideas?