Since I bought my 88 i have not been able to get the temp to go above 125 is this normal?

Aaron

 

Thermostat on the 6.9l and 7.3l motors are set to 195 F.

What gauge are you using? Don't rely on the factory dash gauge, it has a tendency to show lower as they age.

If you have an aftermarket gauge where is your sending unit located? The 7.3l uses a temperature sending unit and a temperature switch. The temperature switch in the front of the drivers side cylinder head (No. 2 cylinder) is for control of the high idle during engine warm-up. The temperature sending unit for the factory dash temperature gauge is located in the block, near the top left front of the engine in front of the intake to No. 2 cylinder (front most cylinder on the drivers side)

Seb.....

 

I'm using an autometer gauge that is in the later of two and the factory gauge also always read right around the cold mark.

 

Both my 91 and 93 factory gauges read "just" inside the normal mark, yet my temps are right on 195 F. Don't trust the factory gauge. Make sure the manual gauge sending unit is properly dipping into the hot fluid. (i.e. make sure the installer did not install a Tee or some other pipe nipple that would take the sending unit out of the hot coolant.

You can Tee in an oil pressure gauge but usually you need to get any temperature probes right into the fluid if you want a proper reading.

If all the above checks out then your thermostat is the most likely culprit for the low engine temps you are seeing.

 

Do you know which Tstat is installed, do not use aftermarket.......could be the clutch fan is locked up and not unlocking. Do the fan test at the address I sent you.....email.

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 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. Replace all items in reverse order......
Manifold bolt torque......... 20ftlbs

 

The clutch fan works fine i can here it kick on and off when towing up long grades so I think that it is the thermostat.

 

I had this same problem in my 87 6.9. It took 3 t-stats to realize the only one that worked is the motorcraft one. At least thats the only one I could find.

 

The temp switch that does high idle and timing advance is located in front of the passenger side head right beside the thermostat. Almost impossible to see with the wires hooked to it and the alternator installed.

The sending unit for the stock gauge is located in the block on the drivers side under the AC compressor.

The one in front of the drivers side exhaust manifold goes to the overheat light on older trucks, or the check engine light on newer trucks.