My 2000 F250 7.3 always runs cold. In the winter it barely reaches the lower mark of the operating range and in the summer it only goes a little above the lower mark. This is my first 7.3 and I was wondering if this is normal? I bought it about a year ago from a broker and best I can tell it came from Huston, TX. Could it be as simple as the previous owner changed the thermostat so it would run cooler in the Texas heat? I just wanted to make sure this doesn't indicate a developing problem.....

 

Make sure it has enough coolant. If the coolant does not touch the sensor it will not register. Up there in a northern clime I might recommend a 203* thermostat. Installing that and a billet outlet would also give you a chance to see if it even has a thermostat. Sometimes folks remove them. Especially PO'd cowboys wrenching and sweating in 105 degree shade. The 203 thermostat is not universally recommended, btw. Generally these trucks run cool, difficult to overheat with normal maintenance. Speaking of maintenance, the coolant needs maintenance, check the SCAs.

 

Before changing the engine in any way, you need an actual temperature reading of your coolant and oil. Get an inexpensive laser thermometer (I see them for about 30 or 40 bucks) and check the temperature at the thermostat housing and the oil cooler (big tube on driver side). Your coolant might be 165-175, and the oil from 190 to 200... if you've driven at least 20 minutes. If you drive short hops and turn the key off... your gauge is likely not lying.

I use my laser thermometer for troubleshooting a lot, so it's not wasted money to get one. You can use it to check brake temperatures, exhaust temps, bearing temps, and electric wire temps.

 

Agreed! I love my temp finder.
Actually used it last night twice. I borrowed my dad's 7.3 and I noticed the engine temp gauge was low never got to the normal mark. I drove it 25 mins home in a mix of freeway and city rush hour. It was about 28°f here in slc. I was concerned. I tried the heater and it was fairly warm, but definitely not hot like it should be.
When I got home I popped the hood to get a reading from my temp finder and in the upper rad hose and coolant reservoir I had a temp of only 115f. Tonight I'll do the same and measure a few other areas.

But in comparison I also measured my truck(a 79 f150 w/ 400m) and the upper rad hose and rad measured 190ish.

I'm thinking of buying him a a diesel site 203° t stat and billet housing.

Hopefully this helps in some way.

 

been very happy with the new stock motorcraft thermostat here in single digits & below zero temps.but imagine the 203 t-stat would take it to the next level.

 

Great point! And they are getting cheaper. I use mine to check tire temps when towing. Just a quick walk around zapping the tires at a fuel or bio stop. A tire with low pressure will run hotter, prompting further investigation.

 

It's possible the incorrect thermostat is installed or the existing one is faulty and stuck in the partially open position.

A new Motorcraft thermostat might solve your issue as well. It's not uncommon for the t-stat to fail in the open or partially open position.

You can use a scan tool to verify. If you have a manual trans truck, then look at Engine Coolant Temp and see if the temp gets up to 195 and then stays there even when the truck is parked and idling.

For automatic trucks, look at Engine Oil Temp (since the coolant temp sensor isn't connected to the PCM...). EOT should be around 200-210 while driving (unloaded) and might cool down a bit when the truck is parked and idling. If the EOT falls down to 170-160 or lower then your t-stat is likely stuck open.