1994 7.3 NA Running Warmer than Normal?

I was parked today idling while waiting for someone and saw the temp gauge at about 3/4 scale. Normally it’s around 1/4. This was after an hour or so driving through town so stop & go. Truck is a 1994 F250 7.3 IDI NA. I shut the truck down and checked it over, it didn’t feel or seem hotter than normal. The overheat light did not come on. Outside temp was about 45F; it’s seen warmer temps before without this issue.

Later on after letting it cool down I did some purposeful test driving and it behaved the same, so something has changed. I had been noticing every once in a while the gauge would drop out, so I bought a new sensor but hadn’t put it in yet. I’m going to start with that tomorrow. Any other ideas what this could be? Is it possible the water pump impeller is rotted away?

Maybe fab clutch? But it did hold the higher temp going down the highway too. Wouldn’t I see it go down on the highway if it was the fan clutch?

I did notice the top of the radiator is hot but it gets cool in the finned area. Even when the top was too hot to hold my hand on, a few inches below it was cool to the touch. Is that normal?

Is the t-stat possibly bad? Should I replace that when I do the temp sensor since I’ll lose the coolant up there anyway? Any considerations or specific bleeding I need to do after I put it back together?

Any puking into the reservoir? Coolant level in the radiator? Have you checked the motor oil for evidence of coolant? The top tank would be exceptionally hot with steam if you're dealing with a head gasket failure. When the truck is cold, remove the radiator cap and check the coolant level. Start it with the radiator cap off and watch for surging coolant, or other evidence of head gasket failure.

The coolant level was normal. No issues when I ran it with the rad cap off. I replaced the sensor (or is it sender?) and it didn’t change anything so it’s not that. The sensor needed to be replaced anyway. Are clogged radiators common? With it being hot on top and cold in the heat exchanger area I wonder if there’s just no flow.

Get one of these so you can see the real temperature. It has the right fittings included to fit the IDI. Put it in the dummy light port on the engine so you can see both the factory gauge and this one:

https://www.oreillyauto.com/detail/.../8242/4299473/1985/ford/e-350-econoline?pos=2

Cubey said:

Get one of these so you can see the real temperature. It has the right fittings included to fit the IDI. Put it in the dummy light port on the engine so you can see both the factory gauge and this one:

https://www.oreillyauto.com/detail/.../8242/4299473/1985/ford/e-350-econoline?pos=2

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I agree with the above. A lot of money can be wasted buying parts when you are relying on the crappy factory gauge. I guess you do know your oil pressure gauge is fake also from the factory and always reads in the middle as long as you have 5lbs of pressure? Get a set of real gauges and put them on it under the dash. They have real numbers that tell you something.

Thank you for the replies. Yep I've heard about the factory gauge being trash. However, it was consistent for so long, then does this, and it's repeatable. I might put in an aftermarket gauge to troubleshoot, but I still think something's off. I thought maybe the upper rad hose was harder than normal when I stopped it today, but that could be confirmation bias and a skewed memory of what the hose felt like 'normally.'

I do plan to get gauges in the truck. Having a real oil pressure gauge in my Ranger saved my a couple of months ago. It's on the to do list but keeps getting pushed down. We are in the process of re-siding our house and today I just found the entire North wall has rotten, moldy, wet sheathing so it looks like that project budget will be ballooning quickly.

Do get a good mechanical gauge before you get too worried about the factory temp gauge. Since my thermostat is stuck open, I still have cardboard blocking about 2/3 of my radiator. Today it was over 70* here. While driving through town, my mechanical temp gauge was reading 190*. Going down the highway, it was reading 195*. The engine temperature was higher while going down the highway because the engine was working harder then it was while driving through town.
The #1 rule here is NEVER take the factory gauges as gospel. They weren't accurate when our trucks were new, and they're not any more accurate today.

Ok I put a mechanical water temp gauge in today and test drove it. Going down the highway empty at 70mph it was sitting at about 210F. When I got back into town the temp went up to about 235F during the half mile or so to my house at 25mph. About halfway down the rad was cold. Lower rad hose also was cold.

bilbo said:

Ok I put a mechanical water temp gauge in today and test drove it. Going down the highway empty at 70mph it was sitting at about 210F. When I got back into town the temp went up to about 235F during the half mile or so to my house at 25mph. About halfway down the rad was cold. Lower rad hose also was cold.

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Sounds like a bad fan clutch to me, but it could be a sticking thermostat too... or maybe it's both. An IDI at highway speeds should be around 180-200F (steep hills can take it above 210) and around town about 180-185, at least in my experience. 240*F is the red line for these engines. Above that and you risk melting the aluminum pistons.

My RV (huge wind resistance vs a pickup) with a weak fan clutch was doing 190-210*F at highway speeds. Slow speeds were fine. With a new Motorcraft fan clutch and thermostat, now it typically does around 180-200 at highway speed.

If it were the fan clutch, wouldn’t the radiator be hot all the way top to bottom? If the lower hose is cold wouldn’t the engine be getting cold coolant and not overheat? Unless I’m missing something there. To look at the radiator I’m planning on pinching the upper hose shut and draining enough to see the top of the finned section. I’m not sure how else to check it. I think the tstat is opening as the upper hose gets hot and the system pressurized as it should. Unless it would if the tstat were stuck shut too?

If the thermostat is stuck closed, the upper radiator hose may get slightly warm, but not hot. I think it's starting to sound like a plugged radiator.

bilbo said:

If it were the fan clutch, wouldn’t the radiator be hot all the way top to bottom? If the lower hose is cold wouldn’t the engine be getting cold coolant and not overheat? Unless I’m missing something there. To look at the radiator I’m planning on pinching the upper hose shut and draining enough to see the top of the finned section. I’m not sure how else to check it. I think the tstat is opening as the upper hose gets hot and the system pressurized as it should. Unless it would if the tstat were stuck shut too?

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From your readings, your engine is not in any danger. It is unusual that it got hot in town. Usually putt-putt-ing around they will cool off. They usually only run hot going high speed down the road or pulling a load.

If you do want to check the radiator, this is how the radiator guy showed me how.

You have to drain the coolant.

Take the lower radiator hose off.

Get the garden hose, and hold it in one hand, while you take your other hand and seal off the large bottom radiator hose outlet. Keep it sealed off and fill the radiator with water till it's totally full.

Then quickly pull your hand off to unseal the outlet at the bottom. He said the bottom outlet should flow full volume and smooth. If it does, the radiator is not clogged.

If it gulps and only flows a portion of the outlet volume, then the radiator is partially clogged.

franklin2 said:

From your readings, your engine is not in any danger. It is unusual that it got hot in town. Usually putt-putt-ing around they will cool off. They usually only run hot going high speed down the road or pulling a load.

If you do want to check the radiator, this is how the radiator guy showed me how.

You have to drain the coolant.

Take the lower radiator hose off.

Get the garden hose, and hold it in one hand, while you take your other hand and seal off the large bottom radiator hose outlet. Keep it sealed off and fill the radiator with water till it's totally full.

Then quickly pull your hand off to unseal the outlet at the bottom. He said the bottom outlet should flow full volume and smooth. If it does, the radiator is not clogged.

If it gulps and only flows a portion of the outlet volume, then the radiator is partially clogged.

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That is a neat trick I never would of thought about doing.




Rock

franklin2 said:

From your readings, your engine is not in any danger. It is unusual that it got hot in town. Usually putt-putt-ing around they will cool off. They usually only run hot going high speed down the road or pulling a load.

If you do want to check the radiator, this is how the radiator guy showed me how.

You have to drain the coolant.

Take the lower radiator hose off.

Get the garden hose, and hold it in one hand, while you take your other hand and seal off the large bottom radiator hose outlet. Keep it sealed off and fill the radiator with water till it's totally full.

Then quickly pull your hand off to unseal the outlet at the bottom. He said the bottom outlet should flow full volume and smooth. If it does, the radiator is not clogged.

If it gulps and only flows a portion of the outlet volume, then the radiator is partially clogged.

Click to expand...

Thanks for the tip, that makes a lot of sense! I will give this a shot as soon as I have a chance.

Sounds like your thermostat is stuck shut , if your radiator is cool in the middle and hot up top the fan won’t activate , signs of a faulty thermostat

squeeze the upper hose if it feels hollow and you can’t tell there is coolant in there , red flag

yes I agree with above that you can’t rely on stock gauges , but from your findings with the mechanical gauge proves your stock gauge is working,

franklin2 brings up a good test for flow on the radiator, if your going to do that test might as well pull the thermostat too and get a new motorcraft one

there is also a way to test the thermostat in the truck without pulling it but you have to drain the radiator