89 F350 7.3 IDI - The temp gauge was ready low (normal for what previous posts say), and hitting the N under normal operation after about 30 min. Pulling a good load (9500 lbs), the heat started kicking up to the O/R range, then clicked up to the A/L range and the red engine light came on. I pulled over checked the fluids (normal), let the engine cool for a while, then drove about 10 miles with the engine light ticking on and off in the M/A range. After letting the truck sit for about 1.5 hours I could put my hand on the radiator or the engine without any heat build up. I put the key in the ignition and the temp gauge still read A/L. I let the truck idle for about 10 minutes with no change. All coolant level was good in the rad and the overflow. I drove back home and ignored the temp gauge (the engine light did occasionally come on). When I shut the truck down, and turned everything off the gauge stayed at A/L. Any thoughts? Is the gauge off, or the sending unit? My main thought is the sending unit as the engine light came on as well. At a few points during the drive the temp gauge dropped back down to N for a few miles, then back up. The Chilton's manual has a list of the ohm reading for certain temps if I want to remove the sending unit, but it does not disclose the location of the coolant sending unit.

Should I put in an aftermarket gauge and sending unit, and if so, does it replace the existing factory unit, or tap in somewhere else? Sorry for the long post. Oh - it was about 75 degrees outside on the trip out and 60 on the trip back.

Thanks.

 

Two seperate sending units, one for the gauge, one for the light.

Front of the drivers side head.



A mechanical temp gauge is the best route.
But it will have to be mounted somewhere besides the dash.
Where are your boost and pyrometer located?

Did you hear the fan clutch lock up when the temp was high?
Definite roar when it locks up.

 

I will drive the truck some tomorrow to check to see if the fan is cycling on/off. As for the roar, the whole truck roars, no muffler (not sure if this is normal or not). The windows were open (going about 55) with the heat on to try to keep the temp down. I could hear/feel the turbo kick in when I took all there was out of the pedal. The fan seams to be on all the time, but I will check. With that in mind, and with the two heat detectors, I guess if both the engine light and the temp gauge are reading high - then, well hence the name idiot light.
Thanks.

 

Fan clutch problems are rather common on these old trucks.
If the fan clutch is not locking up, high temps are not out of the question.
A load and turbo makes that even easier.

 

Check your email, I sent you one.

 

I tried to spin the fan this evening before starting the truck (cold for 24 hrs). The fan would barely turn a 1/4 turn. No wiggle. I started the truck and the fan spun slowly then worked up to about engine speed. I ran the truck hard at about 65-70 mph up and down hills on the freeway. Temp gauge read up to N/O. Fan never kicked on. I pulled over and raise the hood - fan moving about engine speed, rev'd up and fan spun back up to the engine speed, but definitely no roar.

Dave - are the pics you posted from the right rear or front left as you look into the engine compartment?

And if I read your post right - you recommend getting an aftermarket mechanical temp gauge that fits into the sending unit hole.

Thanks!

 

I did the fan test (covered front of rad with cardboard, hooked up a mechanical temp gauge into the old sending unit hole, and heated up the engine). The engine heated up to 235*, but the fan never sped up (it was a little faster than at idle - I was running about 2000 rpm). So - does this mean my fan clutch is bad?

I ordered one today from Advanced Auto - 1 yr guarranty.

Also - when I grounded the wire from the sending unit - the stock temp gauge pegged and the idiot light came on. Same thing happened when I grounded the temp switch wire. What's up with that?

Thanks for your help.

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89 F-350 Crew Cab long bed - 7.3 IDI Hypermax Diesel

 

89 wiring must be a bit different from the 86 model, one wire only does the light and one wire only does the gauge on mine.

I mounted a pod on my dash, volt meter, oil pressure and engine coolant temp.
Boost and pyrometer are pillar mounted, wish I had a triple pillar mount so I could move my oil temp gauge up there as well.

 

I replaced the fan clutch (it was quite painful to get the nut moving on the old one, ended up getting the two wrenches close together and using a hammer handle to pry the wrenches apart. Also, the large pulley wrench uses the bolts on the pulley, so I loosened the nuts on the pulley to give me more purchase (many bleeding knuckles from this experience). I ran the same test with the cardboard infront of the radiator. Temp got up to about 190, the fan kicked in and the temperature wouldn't go up much more about 190. So it worked.

Thanks for your help!!

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89 F-350, dually, crew cab, 7.3IDI, Hypermax turbo.