1994 7.3 NA Running Warmer than Normal?

Here is the top of the radiator. The hose was full of fluid and pressurized when it was hot. It’s better than I expected but still kind of gunky. Further over it’s a little bit worse.

It may be time to pull the radiator and try to flush it out with a garden hose. When you do that, leave the cap on it and turn it upside down. Put the hose in where the lower radiator hose attaches. This will back flush it for you. I would flush it both directions until you aren't getting any odd colored crud out. Then you'll have it about as clean as you can get it.

That’s the next step. A few years ago my son heater core was plugged. We hooked one of the hoses up to a sump pump that was in a wheelbarrow full of vinegar and set the other up to drain back. We recirculated the vinegar through the core overnight and were able to revive it. I think I will try that with the rad after washing loose what I can with water.

My vote on this is thermostat failed- based on similar experience. Would heat up from just normal driving; changed fan clutch and no change. Pulled thermostat and found one of the three tabs that hold the pellet broken so even though the pellet was expanding/extending, the thermostat wasn’t able to open to send the water to the radiator. Not a Motorcraft thermostat- lesson learned.

gfemling said:

My vote on this is thermostat failed- based on similar experience. Would heat up from just normal driving; changed fan clutch and no change. Pulled thermostat and found one of the three tabs that hold the pellet broken so even though the pellet was expanding/extending, the thermostat wasn’t able to open to send the water to the radiator. Not a Motorcraft thermostat- lesson learned.

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If the stat wasn't opening, wouldn't the top hose stay cool and squishy?

bilbo said:

If the stat wasn't opening, wouldn't the top hose stay cool and squishy?

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It would stay cool, but probably not squishy. I think it would still build up pressure in the cooling system. Pressure from normal operation will equalize itself through the whole cooling system. Since your upper radiator hose and the upper part of the radiator was getting hot, then your thermostat is opening. This is the ONLY way that the top of the radiator can be hot while down lower it's cool to the touch. The reason for this is that the hot coolant isn't flowing through the tubes in the radiator very well. If the hot coolant doesn't flow well, then it can't transfer heat to the rest of the radiator. The heat mostly stays in the top tank of the radiator where it goes after the thermostat opens. All of the suggestions about a thermostat being stuck closed are wrong. If your radiator and upper hose weren't getting hot at all, the you'd have a stuck closed thermostat because it wouldn't open to let hot coolant into the upper hose. It wouldn't be a bad idea to replace your thermostat at this time if you want to since you'll already be working on your cooling system and will have it drained enough so that there won't be much coolant come out after you remove the housing.

The description of the symptoms and the pictures of inside the radiator are pretty indicative of a stopped up radiator. If it were me, I’m going to assume the rest of the cooling system doesn’t look pristine. I’m pulling the thermostat housing and replacing the thermostat, and flushing out everything else I can with a garden hose. Maybe even add a coolant filter to catch any of that, that may still be circulating through. I’d even be considering replacing the water pump if it is of unknown age or condition.


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I found out we still have a radiator shop in town and gave them a call. I’ll be dropping it off there for them to look over. I took it off and there are a couple of suspect areas where it might be leaking a little bit. Also, the cost to have it cleaned by them was pretty minimal, if that’s indeed all it needs. We will see what they say.

I know the rest of the system probably doesn’t look much better. But for now I will flush with the hose and then distilled water and call it good. Really I just need it back out of my driveway for now to prepare for the surgery I have to do on my house. Super excited about that, not.

bilbo said:

I found out we still have a radiator shop in town and gave them a call. I’ll be dropping it off there for them to look over. I took it off and there are a couple of suspect areas where it might be leaking a little bit. Also, the cost to have it cleaned by them was pretty minimal, if that’s indeed all it needs. We will see what they say.

I know the rest of the system probably doesn’t look much better. But for now I will flush with the hose and then distilled water and call it good. Really I just need it back out of my driveway for now to prepare for the surgery I have to do on my house. Super excited about that, not.

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Don't be surprised if after they clean it, they say it's no good. They like to rot out at the bottom. Then you have the decision to make, $500 for them to re-core it, $380 from autozone for a new one, or $280 for a aluminum one from ebay.

Yep I’m prepared for that. The top driver side corner looks suspect. They know about it; we will see what happens.

The radiator is indeed no good. Nearby there is one available from a 6.9 truck with an AT. Does anyone know if they have changed appreciably over the years? It sounds like it's the same outside dimensions as the one I had.

As long as it has A/C, I believe that these will interchange between all of the IDI powered trucks. They may even be the same with the first gen 7.3 PSD trucks. The radiators for non A/C trucks are the short, wide ones. This is why I have three extras sitting in my garage with another one out behind it in a truck that still needs to be scrapped out.

bilbo said:

The radiator is indeed no good. Nearby there is one available from a 6.9 truck with an AT. Does anyone know if they have changed appreciably over the years? It sounds like it's the same outside dimensions as the one I had.

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Unless you know that used radiator has been replaced recently, I would not mess with it. They all get old and end up in the same shape as yours is in. If you are strapped for money, it's hard to beat the aluminum ones on ebay. They work good, I had one that lasted 15 years and now I am on my second one.

Well gfemling wins a prize and I have to eat crow. Pulled the thermostat to see how it looked and it’s broken just like his was. No idea what brand it was but a Motorcraft will go back in. Gfemling, If you ever find yourself in Grand Forks ND, I’ll buy you lunch!

Just to follow up, the new thermostat fixed it. Under light load it slowly raises to 190 then drops to just above 180 and repeats. Today we had a killer wind and it stayed between 185 and 190 going into the wind 70+ mph.