This may be a little long winded...(and bare with me...I am semi-intellegent,,,but by no means a professional mechanic)

but I need a little help diagnosing my overheating problem and trying to figure out what to replace next. Funds are a little tight at the moment so I would like to try and pin point the problem as opposed to the shot gun approach of just replacing a bunch of items...

Anyway here is the situation thus far....

1988 Ford F250 Diesel..

Vehicle was operating fine until all of a sudden while shutting off the vehicle I hear a strange noise under the hood. After openning the hood, inspection revealed the fan had unscrewed and fallen off.

Strange I thought..so I just screwed it back on...of course this didnt solve the problem because at my next stop the same thing happened....so I screwed the fan back on one more time and returned home and removed the fan from the truck and realized the clutch had frozen up....

I put the clutch in my vise and was able to free it up..and re-installed the fan back in the truck. I ran the vehicle like this for a couple days until the local parts store was able to order a replacement fan clutch....The truck ran fine...a little on the warm side..but no where near hot...temp gage was right in the middle...

Anyway...after getting the new fan clutch and installing it...the truck started to overheat...not to the point where anything blew up...but after running the truck for about ten minutes the temp gauge climbed up above 3/4 and so I shut the vehicle off and let it cool... while it was running I did check to make sure the fan was spinning etc....

So I figured it was just my luck that the fan clutch I had purchased was defective... I borrowed a friends car returned this item and drove ten miles to another parts store that had a fan clutch in stock and put this unit in the truck....

No - change...after ten minutes of running the same thing happened.... so after cooling off I checked the radiator level..and noticed it was a little low on fluid...so I just added water to top it off...

My next guess was that my thermostat must have coincidently gone out at the same time as replacement of the first fan clutch...I was guessing at this and since the thermostat was only a $15.00 item I figured it was cheap enough to replace...(why do they make a cheap item such a pain in the A$$ to replace)

Anyway after two hours of remove parts, draining radiator fluid (which is now 90% water) and cleaning gasket surfaces I put in the new thermostat and test drove the truck.

Still the same problem...after about 10 minutes, my temp gauge gradually works it way higher and higher until I have to shut the vehicle down and let it cool...

I can extend this time if I run my heater at full blast while driving...but its hot here in FLorida and I really would like to get this problem resolved...

HELP...with what to test or replace next....

Thanks

 

My first thought is restricted air flow thru the rad core. Blow the core out with compressed air (especially if you have a condenser in front of it). This should help. When hot feel the top and bottom rad hoses, they should both be hot. If the lower one is cool then you have restricted water flow thru the rad. Inspect the condition of the rubber seal on the rad cap, the seal has to be good to keep pressure in the system which lowers the temperature. Another possibility is a defective water pump but I have not heard of these giving trouble, maybe someone else knows this. Good luck with it.

 

Thanks for the quick response...

I blew compressed air through it...not much if any debris came out...it seemed pretty well clean and air flow was not restricted.

The hoses were both HOT.....

 

Just another thought, I take it your fan drive belt is in good condition and well tensioned up?

 

Along with that, when the truck starts to heat up, can you hear the fan getting louder while driving with the rpms up? Meaning, is the new clutch even working cause if the lower rad hose is hot, that should mean that you have coolant flow. Im thinking its an air flow issue. Im wondering if the new fan clutches are slipping to much and not enguaging the fan like it should cause you said it was fine until the old locked up and fell off. Do you still have the old locked one? if so, I would put it back on tight and see if it still overheats unless you think its going to mess up your radiator if it comes off one more time.

 

Well this makes the situation worse I belive....

While test driving it this afternoon....The temp gauge gradually worked its way up the scale...took about 15 minutes to get above the half way mark...

I turned on the ac in order to work the vehicle harder and get the temps to raise....a few minutes later I was approaching 2/3 on the temp gauge...

The check engine light flickered for a brief second and then the gauge started falling...it lowered all the way down to just below half...sitting right on the "o" of "normal"...and it stayed there for about 15 minutes or so while I kept driving the truck.

I had to make a stop at a friends house and stayed there for about 45 minutes.

While there the engine cooled down...and on my ride back home I was back to square one...gauge gradually worked its way up to above half and then kept going up until about 3/4 by the time I made it to my driveway...it didn't appear like it was going to drop down this time so I just shut the truck off in the driveway....

talk about a messed up situation....

I thought about putting the old clutch back in...but its in pretty bad shape...all the bearings appear to be gone and it has a lot of play in it...with my luck it would fly off and go through the radiator....plus I figure since I did try two new clutches already...that the chances of both of them being defective was slim...

 

All the belts look in very good condition and have a good amount of tension on them...

As far as hearing anything different while I am driving at a higher RPM..I just hear the 7.3 Diesel roaring away...to hard to distinguish anything else...


When this first started happening I too thought it was an air flow issue...I even thought maybe I put the fan on the clutch backwards...but I'm fairly certain the installation is correct...

especially now since it drove once ok...

I'm thinking maybe a defective thermostat...(I hate to think I have to pull all that crap off again) or two maybe something with the waterpump...or three...maybe a faulty sensor for my temp gauge???

 

All I know is when I hit the road and my temp starts to climp I can definatly hear the fan kick in. It will roar loud expecially if the rpms are up. You will or at least should know when it kicks in unless you have teribly loud exhaust. Mine is somewhat loud and I can still hear it very well. Drive without the radio and ac on so you can hear very well and see what happens.
You could also be right on the tempature sensor issue. Mine is messed up and my engine temp light stays on.

 

Im sure this is a stupid question but Im gonna ask anyhow. Is the fan on right? I dont know if yours is reversable, but I know on a big truck you can use the fan to suck air thru the radiator or push it back out engine side going out. Second off, which way did you blow the radiator core out? When you do that you need to blow from the fan side blowing towards the grill. Then there is the question of was your temp guage working correctly before this happened. Im not calling you an idiot, some people just dont know or think about this stuff!

 

I assume I put the fan back on correctly..the airflow...which is strong sucks the air through the radiator and back towards the engine...

I blew the raidiator core first from back to front..and then front to back and then up to down and then down to up....pretty much every direction....

My temp gauge seemed to be working fine before I did any repairs...although its just the stock gauge, so I am not sure how accurate it was from the start...all I know is it registers a lot higher now...

One thing I have noticed, is that the temperature doesn't seem to rise at a steady rate on the gage...even when driving at the same speed and rpms...it seems to pause every now and again...sometimes for a few minutes..and occastional will even drop slightly......but only once so far did it actually have a big drop and return to normal...the remaining times I had to shut off the truck and let it sit to cool..

 

The cheap thermostat you replaced is what I would suspect is the problem. The only one that should be in there is a Ford Motorcraft P/N E5TZ-8575-C, or The correct one from an International dealer ( don't know that P/N).

 

Its a possibility that I will have to deal with...I'll let you know if thats what it turns out to be...

Thanks

 

The way you speak of your temp guage doing the sudden movements, Id get a new temp sensor and stick in it. A bad one can throw codes left and right

 

Well..after doing a little more diagnosing I discovered the problem....

I found two symptoms that pretty much gave away what the problem was....

Figured I would list them to help anyone else out in the future who might run into this problem....

Here is what I knew thus far....(have owned the truck for 3 months thus far)

Truck was running OK for the most part...

Then while driving one day the fan fell off when I turned the engine off..which was the result of a locked up fan clutch....

I replaced the fan clutch and the truck started overheating.....

Figured the fan clutch was bad so I replaced the new one with another new one....

My next step was to replace the thermostat hoping to solve the problem...

Still overheating...while sitting at a light it seemed to hold in temperature...only under load or excelerating did the temp really rise drastically....

I flushed the system...but the fluids which came out were fairly clean, with little or no debris....

Both hoses would get hot during testing....

The two additional things I now noticed on further inspection....

1. The lower hose would crimp while increasing throttle....

2. With the radiator cap off fluid would rise up and out the top of the radiator during exceleration even when the temps were not that hot..

Ok....before I reveal what the problem was...anyone want to take a guess at it.....

 

I was thinking all along: Air in the system. Would have said it earlier but I just checked out this thread.