Hi all,

I'm new to large pickups and also to diesels (as well as this forum), so please bear with me here. I have an 89 F350 dually diesel (7.3) with 4:10 rear and 5spd manual (2wd). The problem I seem to be having is that she seems to want to overheat during any kind of extended driving. By that I mean almost any "cruising" for more than about 10 or 15 minutes at a stead 2000 rpm. Mostly I see this on the highway, but I have run into it during a drive uphill in 4th gear where 5th gear just wouldnt cut it.

Basically I can see the temp start to climb to the "M" and "A" on the temp gauge where it says "Normal"....sorry if this is an amateurish assessment here, but since there's no degree marks on the gauge this is all I have to go by. When driving around town or on back roads where I can keep the revs down to about 1500 she stays around the "N" or the "R" part of "Normal". The needle seems to climb pretty fast, and I've never let it get to the end of "Normal" because there's not a whole lot of room between the "L": and the redline of the gauge. It also drops pretty fast when I let off the pedal and coast for a bit.

Is there something wrong here, or is this normal and I'm just being a wuss? This is by far the largest vehicle I've ever owned...and the first diesel...so I'm not sure if it's okay to run hot. To me, it seems like something is dragging, maybe in the rear end, since acceleration is a little sluggish...I'm going to pull the rear brakes soon and check them out.

Oh, and the coolant is full with no known engine issues as far as I can tell...I do have a throw out bearing on its way out though, I'm pretty sure.

Thanks for any help!
RJ.

 

Definitely doesn't sound right to me. I would check the coolant level on it and top it off if necessary. If you think the fluid is old then it's not a bad idea to change it but do it yourself. Don't pay to have it flushed out, they just recycle other people's old coolant into your engine a lot of the time. There is also a special additive that you need in the coolant for a diesel, make sure you use it.

 

Check your fan clutch...almost identical problem with my truck and the fan clutch was bad. Replaced it and its cool as a cucumber even after 5 years. Hope this helps!
Roger

 

Thanks! I'll double check the coolant to see if it's dirty....didnt seem it but maybe I overlooked it.

Any thoughts on how to check if the fan clutch is bad? I actually havent been under the hood all that much yet on this truck, so I'm guessing it's just a viscous coupling clutch, right? I'm kinda hoping that's the issue since it should be a pretty easy fix (I'm guessing).

 

If it's just overheating on the highway then it's not your fan clutch. Anything more than 35 MPH or so and the fan does absolutely nothing. It can't, because it's never going to draw in more air than is already being pushed through the radiator by the truck moving down the road.

I wondered how long it was going to take for someone to suggest this though.

 

I was thinking that too, but again, wasnt sure b/c this is my first diesel. I'm still leaning toward dragging something in the rear end. The truck will sit and idle forever with no heat issues, its only when I'm moving at a steady 2k or 2250rpm that there's the problem. I would think that a truck with a 4:10 rear and a few hundred ft/lbs of torque at the wheels should be giving me a little more acceleration from a stop than what I've been getting.

 

Then your fan clutch is fine. I would service the cooling system and then see where you are with it.

Also maybe someone who has more experience could chime in.... but I think you should have more power than that. Does it have a turbo on it? I know some didn't come with one and that could be the problem too. I've heard the non-turbo IDI motors could be kinda sluggish.

 

sounds like the water pump is bad or a hose is collapsing and not letting the water through

 

If not the fan clutch, then jack it up and see if the wheels spin freely. This is also something that's often overlooked-could be a stuck caliper up front or possibly an over-adjusted drum in the rear. + 1 about checking the lower radiator hose as suggested above^. I've had the spring inside literally disintegrate and no longer be effective. Water pump *could* be bad but its the least likely of all. Get a new Ford Tstat and replace just because its cheap. Test the old one in the pot of water on the stove trick. Lastly, check your timing to make sure its dead-on.
Roger

 

its a non turbo, yeah. If this is a clue to anyone, I seem to be doing about 65 on the highway around 2300 or 2400 rpm. This is just an estimate since all I have to go by is my tach and my gps (speedo is busted...working on that too!). Should the revs be lower or is that about right? This is only loaded with about 250lbs in the bed.

And I'll check the coolant this week and service if need be. Anyone know of the additive that anydm mentioned?

Thanks again for the help

 

that sounds about right with 4:10 gears

 

Haha... you want him to check the timing on a diesel?

I bet it will be spot on!

 

D'oh!!
Roger

 

I finally got a chance to go under the hood today and guess what...LOW coolant in the rad and reservoir tank. How low? I'm not quite sure, but the tank was empty and there was no coolant to be seen in the rad. Good thing I rarely drive the truck (not my daily).

I am going to do a total flush this weekend...should I just replace the system with green antifreeze with the anti-cavitation additive (hooray for research!), or can I go with the extended life stuff (seems it may only be for powerstroke diesels?). I'm going to do a search right after I hit "Submit Reply"...but any input would be awesome!

Thanks again,
RJ

 

i would try replacing the radiator cap.. could just be a bad cap.. could be why you lost the coolant or it could be a leak somewhere in the cooling system.

diesels make most of their heat while they're working, not idling...