Join Our Ford Truck Forum Today

Document your Ford truck project here and inspire others! Login/Register to view the site with fewer ads.

96' F-350 7.3 ambulance overheats & needs a doctor

I have read through the threads but I'm at a loss as to why my favorite vehicle is overheating. I'm hoping for some good feedback so please sit back and enjoy the misshaps of Ajaxx (that's me) and his Ambulance (that's the patient).

A few weeks back I made a trip from So. Cal to Las Vegas and when I went over the huge grade outside of Baker, CA I overheated 3 times. I never let it peg out on the temp gauge but would pull over when it got to 3/4 hot and let it boil over and cool off. Then I would add water and I'd be ok for another 15 to 20 miles. Once I got over the grade, my overheating problems were over as it only seemed to overheat while climbing a grade.

In fact, while in Las Vegas, I'd leave the engine idling and crawl into the back for a good nights sleep with the A/C running throughout the night. After 10 continuous hours of that for 5 nights, the temp gauge never climbed beyond 1/3 of the way, which has been the normal temp for this truck for the entire 6 years that I've owned it.

While in Las Vegas I found a mechanic who was not a diesel mechanic but he did find that it had a bad fan clutch. I am pretty sure it was bad because my truck never had that fluctuating fan speed like it does now. It almost sounds like a jet engine when the truck is really under a load or going up a hill. However, this apparently did not fix my overheating problem because on the way back home I still over heated 3 times.

When I got home I Googled my problem and did a lot of research. I even Talked with a retired Ford mechanic. The info I found was that it could be a head gasket but doubtful. I was told iit could need the oil cooler flushed but I couldn't find a local shop that would do it.

I was also told that I may just need to flush out the radiator. I did the flush and everything came out very clean I then filled it with the correct ratio of coolant and distilled water. I even added 16 ounces of the recommended Ford radiator additive which apparently has something to do with electrolites and protecting the cylinder walls. Maybe a Gatoraid for Ford diesels.
It was also suggested that I powerwash through the radiator coils and I did that too. And as a final step I replaced the cap on the degas tank as recommended.

Around town it was now running great with no heat issues. A/C still worked great too as it always did. So now it was time for the true test and try another trip to Las Vegas.

It just so happened that my new Vegas trip was beginning on one of So. Cal's hottest days of the year. It was a dIsaster. I didn't even make it to the steep long grade outside of Baker, CA. I didn't even make it even up the grade leading into Victorville, CA (which is about 80 miles away). The temp gauge went past half way just going over the 241 toll road leading to the 91 freeway which is a hilly climb but only 3 or 4 miles in distance. On the grade 26 mile before I got to Victorville I decided to turn around and limp it back home. Total amount of times that I needed to pull over before the temp gauge pegged out was 6 times but I never let it boil over until the last time.

Also I have to tell you that the truck was empty weight but just that 162 mile trip burned a total of 19 1/2 gallons of fuel which is the worst mileage (8.3 mpg) I have ever gotten.

About 3 miles befpre I finally got home I noticed a noise under the hood that sounded almost like a belt issue. Also I forgot to mention that 1/2 way back home, the a/c stopped blowing consistantly cold air (this was now at night and the outside temp was in the low 70's). I shut down the a/c and tried it again a little while later and it no longer produced any cold air at all.

When I finally got home I popped the hood and found smoke coming from around the a/c compressor. The belt was fine although it was hot and very very tight with absolutely no play in it. The belt did have the required 1/2 inch play but now there was no play at all. I'm not sure if the heat caused it to tighten up or if the mechanic that replaced the fan clutch did not adjust it correctly.

After the smoke subsided, I restarted the truck and noticed that the a/c fan clutch and pully assembly were frozen completely. The belt was just dragging across the stuck pulley hence the source of the smoke. The clutch and pully were very very hot. I shut the engine down and let it cool down completely (about 3 hours).

I restarted the engine and everything appeared to be working fine including the a/c pulley and clutch. I decided to turn on the a/c and see if it would work now. It was blowing lots of cold air but I did notice that the compressor clutch would engage and run for about 10 seconds and then disengage for about 10 seconds. It did this continuously. Not sure but I don't think this should be happening.

So here's my thoughts. Could my problem have been this a/c clutch/pulley assembly all along or is this just another problem popping up? Was the way too tight belt my problem? I think the stuck pulley could explain the poor fuel mileage but I'm not a mechanic. Maybe I have more than one problem now.

For weeks I have been trying to get a mechanic to look at it but the only one I can find here in town (San Clemente) wants about $155 an hour for labor and at that price I could not afford much. I really need an accurate diagnosis though, just not at that price. Does anyone in the area know of a good honest affordable deisel mechanic I could have take a look at it?

Radiator flushes and replacing the thermo are all within my abilities but detailed repairs or figuring out the problem seem to be over my head. Any insight or help you can offer is greatly appreciated.

Thanks a lot and sorry for the long post but I wanted you to undertand exactly how my baby has been acting.

I don't know if this makes a difference but about 6 months ago I switched to synthetic oil. Also the thermostat was replaced with a 195 degree thermostat when the fan clutch was replaced.

I Love this truck, just need a good diagnosis and a good doctor.

Ajaxx

Truck Details
96 Ford F-350
7.3 diesel,
Automatic with overdrive.
Body style: Ambulance
Miles: 131k
bought it at 105k, owned for 6 years
Oil: 14 1/2 qts synthetic oil and filter once a year.
Coolant capacity according to the Ford Service manual 23.5 qts. However whe I did the radiator flush it only took 17.5 qts.
Additional: I Always use Lucas diesel additive as recommended by several commercial truck drivers.
 
Last edited:

Fellro

Moderator
Staff member
A few thoughts here:
Thermostats unfortunately always work even when new, so it is possible you have a failed/improper unit. I can't say for certain if that issue plagues this diesel, but I do know it did cause troubles on the predecessor diesel motors, as well as the 351M/400 motors. The aftermarket doesn't always get it right unfortunately.

How did the radiator look on the inside when you flushed it? Was there much corrosion? Many times the home flushes are not effective, and removal for professional boiling and chemical cleaning are required. The unfortunate truth these days is that is can be less cost to just buy a new one.

These diesel motors are strong enough to be able to twist the mount and shaft off of the a/c compressor if the bearing were to totally fail. I don't see that the bearing could cause this much trouble to that level. I am impressed the belt held up. The pulsing of the compressor would be associated with a low charge most likely. Have you by chance noticed if the truck seems harder to start? If the bearing were dragging that bad, it should show up then. I had an alternator force a no crank condition on my 6.9. I cut the v-belt to it and drove on home, about 20 miles...
 
When I flushed the radiator everything came out very clean and when I looked inside the radiator tank with a mirror it looked clean, Almost as if the radiator had been replaced before I purchased the truck from the fire department.
I noticed that the original thermostat was rated for 203 degrees and the aftermarket one that I replaced it with was rated at 195 degrees. I guess I should just go ahead then and buy an original thermo from Ford.
I have not had any problems with hard starting but the a/c clutch is making a noise and has been for over a year. I thought it was a pulley somewhere that was making the noise but I never could determine which one it was. Then when the clutch locked up the noise stopped so I'm assuming that it's the culprit.
As far as the ac pulsing I give it a charge once I fix the clutch. Do you know if my 96 uses 134 or was that back when they still used R12?
 

Fellro

Moderator
Staff member
As of 94 most vehicles use R134. You can also get the thermostat from an IH/Navistar dealer.
 

dustybumpers

don't play well w others
The a/c is a separate issue, probably the bearings locked up in it, and you will need to replace the compressor.

When the engine is running, and you look down into the open cap, do you see coolant moving?
I'm betting your water pump has decided to fail on you
 
Ok, I guess it could be the water pump. Tthe radiator doesn't have a cap the only cap is on the degas tank. I did however feel the upper hose and it does feel like the thermo is opening and coolant it going into the radiator but then maybe not.
One thing that has puzzled me though is that when I flushed the radiator I only got out 4 gallons (16 qts) of coolant/water. The Ford manual states that the coolant/water capacity is 23.5 quarts. When I filled it back up it only took 17 quarts of coolant/water. I just assumed that the manual was in error but is it possible that the pump was not pumping out the coolant in the block? This would be great if all I needed was a water pump (and the a/c clutch of course).
dustybumpers When you say I need to replace the compressor do you mean the entire compressor or can I just get by with replacing the clutch assembly? The compressors that I've looked at online all only carry a 3 month warranty so I would just as soom keep the one I have and replace the clutch if possible.
 

dustybumpers

don't play well w others
The block holds the rest, so you did half of the system.

Water pump on a van is no fun


I would check and see if the compressor is locked up, I've never had just the clutch lock up. If you replace the compressor, be sure to replace the dryer too
 
Thanks Dustybumpers
It isn't a van though, it's a F-350 truck with a ambulance box on the back but still probably not a fun job.
I've been a domestic refrig & a/c tech for years so I do know about the dryer but I would prefer not to have to open the system if I can avoid it. The a/c does work and blows cold but eventually the clutch will lock up after a long time of running. How would I check to see if the compressor is locking up? Never worked on a truck ac before.
Also without a radiator cap to look in is there a way to verify the pump is bad? What if I disconnected the top radiator hose and ran the truck til the thermo opened would that tell me if the pump is pumping? How much water would I see coming out the hose? Like a fire hose or what?
 

dustybumpers

don't play well w others
It would empty pretty quick if the pump is pumping. not so much if not. Spraying glycol in the air is a BAD idea. Glycol is poisonous,and can kill if ingested.

If the pump is bad, it won't keep up with the heat load.

Take the belt off the compressor.

If the pulley wobbles around, it's the clutch

turn the pulley, it should be free.
Unplug it. turn the key on, and plug it back in, it should click
Turn the pulley. it should turn, but with pressure on it

If it don't turn at all it's compressor

My town car ate the clutch up , and I replaced just the clutch, one year later, the problem was back, so I replaced the compressor. No more problems
 

john112deere

caffeine junkie
Staff member
10,807
405
central Vermont
I wouldn't go throwing parts at it based on this...but a number of years ago I helped a friend with a very similar problem.

'95 PSD, getting hot pulling grades with a heavy trailer. Conditions were pretty tough (hot, heavy and steep), but he knew his truck and it wasn't normal.

T-stat and water pump replaced, chemical radiator flush, but the problem remained. He eventually yanked the radiator and found it so plugged with what appeared to be dust (desert southwest) that it just couldn't cool effectively. The chemical flush hadn't touched the crud built up in it.
 
Take the belt off the compressor.

If the pulley wobbles around, it's the clutch

turn the pulley, it should be free.
Unplug it. turn the key on, and plug it back in, it should click
Turn the pulley. it should turn, but with pressure on it

If it don't turn at all it's compressor



Well I finally got some time to test the clutch/compressor and the bearings in the clutch are really worn. The play in the clutch is extreme to say the least.

When I removed the belt and clicked on the a/c I was still able to turn the clutch but it did have resistance. So based on what Dustybumpers suggested my compressor is still good. However, the bearing is so worn that I am worried that it may have eaten up a shaft. If that is the case, can the shaft be replaced without opening the system? Also according to the ford manual I am going to need several special tools to replace the clutch. Does anyone know if Autozone loans these tools without my having to purchase them first or is there a place that rents the tools I'll need?

I also used a infrared thermometer are read the radiator temp after the truck had warmed up and the thermo had opened. I found some areas of the radiator showing temps of 130 plus degrees and other areas showing temps around 90 degrees. Based on this I am assuming that the radiator is indeed plugged so I will also be replacing the radiator as well as the drive belt.

If you guys have any more comments or tips prior to my starting the work, it would be much appreciated. I intend to do the repairs at the end of the week when I have some free time. Wish me luck and hopefully I'll be on my way to Vegas next week. I will post the results of my efforts once I complete the repairs and give it a good road test.

Thanks everyone for your help I could not have done this without this forum.
 

dustybumpers

don't play well w others
Not to spend your money, But I would probably replace the water pump while the radiator is out.

The bearing in the clutch is worn, but probably not passed the seat. You will have to remove that part anyway.
 
Yea I agree I should go for a water pump too but I only have $300 so it will have to be my next repair. If I shop wisely I should be able to find a clutch and a new radiator for the $300.

Really need the clutch now because after it heats up it locks and prevents me from starting the truck. This happened for the first time last night at the gas station. After everything cooled down it started right back up. I'm thinking that this clutch is why my gas mileage has been so bad lately (only about 8 mpg). I think it's really putting a load on the motor but not being a mechanic I'm not sure.
 

dustybumpers

don't play well w others
Clutch kit from ford runs about $50 something.

Shop around for prices on the radiator, diesels are salty.

Last water pump I got for a 5.0 ran me around $18
 

Fellro

Moderator
Staff member
Ok, I am confused a bit here, you are thinking the clutch fan is causing you to have a hard time starting the truck? Sorry, but it has no effect whatsoever, and won't hurt your mileage that much. Sounds more like a heat soak problem on the starter than anything to do with the clutch fan. At most 1-2 mpg loss there. Doubt it would even be that much.
 
Dustybumpers,

I sure would like to know where you found those parts for that cheap. I just spent a full day looking for the cheapest way out and the lowest price a/c clutch kit I could find was $99, the radiator for $140 and the water pumps are going for $140 for a rebuilt or $180 for a new one.

Fillro,

It's the A/C clutch not the clutch fan.

So here's the latest with my efforts:

Broke down in a Walmart parking lot and ended spending the night in the back of the ambulance. The next morning I discovered that the a/c clutch finally just froze up preventing the belt from turning the starter. The belt had also been trashed. I then took the clutch hub off of the clutch pulley and what I found was a graphite factory. The ball bearing on the clutch pulley was completely gone except for a bunch of metal powder and the balls that were actually wedged in between the shaft and the pulley causing it to lock up.

I had thought that removing the clutch hub was going to be a big deal requiring a special puller but I could not have been more wrong. It was one of the simplist things I have ever done. One center bolt and it pulls right off. By the way, the shaft turns freely so no compressor will be required.

Tomorrow I will pick up a clutch kit and belt that I had to be special ordered. It appears that since it is an ambulance, a special belt is required. I also need to buy some snap ring pliers but other than that, this repair should be a piece of cake (knock on wood).

My thinking is this. The clutch bearing was so far gone that it must have been a heavy load for the engine to drive the a/c pulley even when the A/C was off, so maybe (hopefully), the only reason my truck has been over heating is because of the worn clutch bearing. I know it's a stretch but I think it 's possible. Since I don't have a lot of money to fix things, this would be ideal for me. All I would need to do is buy some more coolant (3 gal cost about $40) for the 3rd and hopefully last time. If after I test run it (by driving to the mountains) it still overheats, then I have just enough money to replace the radiator. When I get a few extra $$ I will be also replacing the water pump.

Stay tuned I will keep you posted and DustyBumpers, if you really know where to buy a water pump for cheap, could you please tell me where. The cheaper the price, the sooner I can replace it. Thanks.
 

Fellro

Moderator
Staff member
When you get enough drag, it will draw power. I have seen where the bearing hub got so hot that it melted the mounting boss right off of the compressor. I have seen alternator bearings stop an engine at a stop light, and act like the motor was locked up. My 6.9 seemed fine until I shut it off, then it wouldn't turn over again until I cut the belt. It shouldn't have drawn the fuel mileage down quite like that, and still shouldn't have made it overheat, but I guess stranger things can happen.
 

dustybumpers

don't play well w others
Rockauto.com has the radiator for $112.89


water pump for $64.79
 

Ford Truck Articles

Top