Ok I have a 91 F 150 5.8L 4x4 and it overheats under load. I pulled the clutch fan assembly and replaced it with 2 - 14" electric fans. but it still overheats. One fan is controlled with an adjustable thermostat and the other is on a toggle. I replaced the thermostat and it has a new radiator in it?

I was told to put a cooler stat in it and or underdrive the water pump. Does anyone have any input for this delima.

I use the truck mainly for offroading. Climbing hills, muddin, etc. But normal driving i runs about the O on NORMAL...


Thanks
Doug

 

Does it have a spring in the lower radiator hose to keep the hose from collapsing? How about timing set properly? You didn's say if it was auto - larger trans cooler may help. Just some ideas.

 

i haved that problem on my 4.9 but it is the clutch fan

 

Does it only do it under load? Is it ok when driving normally, at highway speed and in the city? What ratio of coolant to water are you using? And like 95X15 asked, is your timing on the mark? 10° BTDC with the spout off. Check under your oil cap for any whitish residue as well. What kind/viscosity oil are you running? Do you have an auto or manual transmission?

 

The lower rad hose does have a spring in it. I have an auto with an external cooler but the tranny runs throught the rad then the cooler. Not sure if I should just run the cooler only? I havent checked the timing yet but I will. The coolant mix is around 50/50. I am going to add some of that wetter water to it and see if it helps. As for oil have valv 10/40 high mile with 1/2 qt of lucas. Also gonna add an external temp gauge to see if it is really running hot.

When Im out wheelin I notice the temp gauge jump alot. Like from the O to the L in a blink of an eye. Then it bounces around and finally stays around the L, which makes me think the thermostat is failing. Then it gets hot but if I take off down the road and drive normal it cools back down to normal??

Im going to tuttle creek this weekend so id like to get it under control somewhat since thoughs hills r killer sometimes. any input will help

Thanks for the replies
Doug

 

Hmmm.... I really like the Lucas transmission addative. I use it on the recommendation of a long time Ford mechanic and have for years. I'm not so sure about the oil treatement though, I've heard pros and cons. If the gauge is jumping it generally means that the thermostat is reacting. What temp stat did you put in when you changed out the radiator (per original post)? Did you check under the oil cap for any whitish residue? Any engine that is tasked hard will run hotter by necessity. I think the manual gauge would be an excellent verification for you to diagnose the problem.

 

I just put a new transmission i in feb. I will be putting the lucas in when i do a tranny service in the future wanted to break it in before I added it. I believe its a 190 stat. I was told when u over heat u usually mess up the stat and its good to change. I just checked the cap and dip stick nothin out of the ordinary.

Doug

 

Great about the cap/dipstick. Get the gauge installed and let's see what it says, okay reads. Severe overheating can do terrible things to an engine. Springs are tempered at around 1,350° before quenching. Repeated overheating can cause springs to fatigue prematurely which would let the stat open prematurely, not go to a higher temp. I think you are going in the correct direction. It might be a good idea to install a B& M auxilary transmission cooler is you're running on the factory cooler and working it that hard. The B&M will be about 400% larger and you can run the fluid straight to and back from it. I'd think about that after I got specific numbers from a mechanical gauge. Changing the stat is a very cheap, simple move that may benefit you. Fordfuelinjection.com says not to go under 180°. You might think about a 10° cooler stat. Even then, the degree of opening does not limit the operating temperature, it simply opens sooner and circulates sooner and can run cooler. I am probably doing the wrong thing by running a 160° thermostat in my F250. According to the mechanical gauge my operating temp on a summer day pulling a gooseneck is around 195°-210°. I've been running it for about 100,000 miles and really haven't had a problem. It was done when the chip was installed. I am NOT recommending that you go that way. I've changed a few things on the truck and this works for me in a mostly hot climate in Georgia.

 

try a new sending unit for your temp gauge. a fualty sending unit will cause it to read high or low, or jumpy