Hi Ya'll
Just wanted to seek a little advice. I have been dealing with some cooling issues on my '88 7.3 IDI for the last year or so. My temp gauge gets close to red lining when I run it hard even without a load or pulling my 10,000 lbs RV at as low as 35 mph going up hills here in TN. I comes back down after taking it easy on her or idling but I just don't think it should be doing that at all. Here is a list of things I have tried all to no avail to top to stop this. I started with the easiest first and now I am starting to run out of ideas:

1) Changed radiator cap
2) Flushed and Bled Cooling system. Left idling to 2 hours without radiator cap to try to get the air out. No bubbles after the first hour really.
3) Replaced almost new Thermostat with the Motorcraft Thermostat. Read and learned from this forum about the difference and could see it when I installed it.
4) Replaced Water Pump
5) Replaced Fan Clutch. Nearly knocked myself out doing it. LOL. Once that sucker gave way I popped myself in the jaw and am still hurting from it.
6) Repeated step 2

I guess normally the next thing to consider be the head gasket but I do not have any of the other symptoms. There is no oil in the coolant, there is no water in the oil. But maybe I am in denial because I will admit a head gasket job is more than I want to take on right now.

Anyway any advice is appreciated. This is a a great forum and most the time I just really enjoy reading it rather than watching TV in any spare time that I am not working in one way or another.

I would like to give a big THANK YOU to any veterans out there who have served. Without you none of the things we take for granted everyday would be possible.

 

Is your coolant boiling when it gets hot? Does the fan lock up and really roar when it's reading so hot?

You said your gauge is near the "red"?? Sounds like you're basing all this on the factory gauge. That gauge is nothing more than a dummy switch, mostly on/off.
Get a real gauge or at least a infrared thermometer and when its close to red check it out the radiator hoses with the thermometer.

Once you have real numbers to go off of you might just find out she's running good. Or not. But its important to get those temp numbers.

 

Ok. Yeah I don't think the coolant is boiling and the fan seems to be about the same as it always is even with the brand new fan clutch. Everything seems to be good except for the reading on the gauge. I'll get a infrared thermometer and check it out. What is the max temp I should be seeing? Thanks!

 

How does your radiator look inside? Maybe someone used stop leak or unsoftened water, mixed corrosion inhibitors/phosphate coolants or something. A new radiator would be my next step. I bet the cores are partially plugged. First step would be get a real coolant temp gauge. The highest I've ever seen in my truck was 210f but it's all flat land here

 

Step 1, install a true temp gauge. As has been mentioned, stock gauge is useless. Then, assuming the new gauge is confirming what the old one is saying, I'd say the only two things left on the list (assuming all the parts you've installed are good) are the radiator or the coolant hoses. If the radiator looks like a science experiment in there, then that would be a good place to start. If it's OK, there are occasional reports of folks having problems where the lower radiator hose sucks itself closed and stops allowing the coolant to circulate. It's usually because the hose was replaced with one that doesn't have a spring (either internal to the hose or integrated into the hose body itself). Long shot, but it has happened before.

Mike

 

The hoses are good I forgot to mention I replaced those as well. The new one did not come with a spring so I took it out of the old one as it was ok. I just ordered a infrared temp gun on amazon and will be interesting to see what it reads. I had not thought about the radiator itself since it seemed to be circulating ok but that does sound like a logical next step if the temp reads too high. So it really should not be anything higher than about 210? Is that a good number to draw the line? Thanks a bunch.

 

If we pretend your cooling system is intact and totally functional, then the water temp should be maxing out around 220*F. I mean if you are running it stupid hard. (This is also dependent on coolant percentage to water)
But just driving around it should be stable right at 195-200*F.

If you go the thermometer route one coolant hose will be hotter than the other. I think it's the lower hose that should be hotter but can't remember which one currently.
Write down both numbers, one great way to easily see if your radiator is working properly is to get the difference between those two numbers. It should be around 15*F, if it's say 5* more than that you may have a blockage. If much less, t-stat is sticking open.

 

With the sensor for my aftermarket gauge in the stock 'OVERTEMP' port, I run right at 195°±5°F unloaded all day long. Given that I use a stock Motorcraft thermostat (supposedly a 195° thermostat) and the rest of my cooling system is fairly new, I would say that's what you should expect. The only time I regularly see above that is if I'm running it REAL HARD, mainly when towing up a grade. Then, getting up to/around 220° can happen but the fan clutch kicks in and does a good job keeping everything in check.

210° while not towing would seem high IMHO..

Mike

 

I've seen 210 not towing but that's with ac on, 90f out, idling in traffic, I have a huge water intercooler radiator in front of my truck, and 4 electric fans in place of the stock clutch fan. When I'm moving on the highway I see about 200 with ac on at 90f.

 

top rad hose should be hotter than the lower hose. lower is coolant into engine, top hose is coolant into radiator.
to test radiator condition, fire up engine and get it to operating temp with radiator full and cap on.
with infrared thermometer, shoot the radiator core. it should be hot on top, and cooler as you go down to the bottom.
if you have cold spots, or the same temperature all the way down in spots, that means those tubes in the core are plugged.
my bet is you are going to find that half of the radiator tubes are plugged.

 

I had similar issues and found out that my radiator was plugged up partially and was leaking internally. The solder around the core's tubes was badly eaten up. My Van is a 1993, and the radiator was original. A local repair shop ordered me a new core and rebuilt my radiator and oil cooler (about $765 parts & labor). I'm sure she'll run cool as a cucumber now!

 

By the way, I only went that route because I didn't trust that those $450 3 row radiators from Napa or O'REILLYs would cool my rig, and I was afraid of putting in one of those aluminum radiators using my high pH coolant. This radiator rebuild came with a 3 year warranty and I have a heavy duty 4 row brass radiator. By the way, the new core is 1/8" thicker and a lot heavier than the original one that it replaced.

It's supposed to be 107°F here this Sunday...that should be a good day to test it out...

 

Well fella's thanks for all the replies. Here is an update. I was excited when I got home from work today and my infrared thermometer had arrived. It is a really cool tool which I can't believe I did not already own as it was pretty cheap ($15)

I quickly got out and started up my rig grabbed my hound for companionship and ran it hard up a bunch of hills and back about 10-15 miles total. The temp gauge was doing the same stuff as it had been getting to about the n and then going to halfway and then going over to right next to the red line. So it was close to the red line when I pulled back into my drive. I then used my new toy to check the temps:

Upper radiator hose: 196
Radiator itself at the top: 220
Lower Radiator hose: 176

The new fan clutch I installed was not even kicked into 'overdrive' with this.

So from these readings to me it seems like I am in good shape but this weekend I'll hook up the trailer and do the same thing and see what happens. I do like the suggestion about scanning the radiator from top to bottom as well and will do that next time too.

I'm also still considering replacing the radiator with a new one anyway then my entire cooling system would be new. I am also going to look into a good gauge and new sensor because I think I have proven out that I am not getting very accurate readings. Does anyone have any suggestions for a either radiators, gauges or sensors that are better then others? Also do you think if I change our the radiator I should also change out the oil cooler as well? I'm about due for an oil change anyway and was wondering how involved of a project it would be.