I have a 1995 f150 ext cab 5.0 with 4 speed auto w/ electronic overdrive. the truck always ran right on the "N" in NORMAL on the temperature gauge. I drive the truck about seventy miles each day and it has always ran at a consistant temp. One day, took about 15 miles to warm up as opposed to the usual 5 mins in the drive way. Once it warmed up the temp kept fluctuatin between the N and the L in normal. Ford says this is perfectly fine, but with 120k miles on it and this being the first time it has done this, i do not consider this normal at all. here is a list of things i have checked/replaced but it is still fluctuating. It will heat up when i am in the throttle and cool down when I have my foot out of the throttle.
- checked gauge, grounded went to Hot, disconected went to Cold
- replaced temp sending unit for gauge, not computer.
- replaced thermostat and checked that it open at 195 before installing
- replaced fan clutch
- replaced radiator cap (13lbs)
- coolant was flushed about 2 mos. ago and appeared very clean when drained for T-Stat.

I do not know what else it could be. really driving me nuts. Whem it is running on the Hot, the upper hose reads about 160 with infered thermometer, when it is running Cool, it reads about 120 the coolant is actually warmer ,but that it the temp of the hose.

any help would be great

Thank you in advance and sorry abou the length of the post.

 

The only thing I can think of is the cooling fan.
Sounds like its not functioning properly; it’s a viscous type fan.
When hot, at idle.... it should be blowing hot air away from the radiator at a good enough speed.
Also make sure the thermostat is installed properly, the spring and pellet should be towards the engine…not the radiator.

 

the fan is functioning properly i think. i put a sheet of cardboard over the rad with a 6'' hole over the center of the fan clutch(new one). once the temp heated up, you could hear the fan clutch kick in and get louder.

Today i installed a new t-stat (192*) tested before install and still the same problem.
I am thinking about running a heater hoe from the output to the input on the block for the heater core. this will eliminate the heater core. i am going to do this because i think the only thing it could be is a partially blocked heater core. eliminating it would only make the t-stat open more and the fan clutch kick in more often but the temp should not be any higher or fluctuate if the heater core is to blame.

Any thoughts or suggestions?

thanks again.

 

also, i just noticed madman, that you are from plymouth. i am from duxbury. know any good radiator shopsaround here? i usually go to ride tech in kingston or bennet tire in duxbury. i went to cape auto body and service in plymouth but not very impressed with them. Thanks again in advance.

 

I have a very similar problem. I have replaced 5 thermostates, one fan hub, radiator, hoses gauge sender unit, tried a mechancial gauge that read exactly the same. I am at the stage now that I just ignore it as it always comes back down in temprature within a minute or less. But it certinaly gives me worry's when it goes up. I have found that some times it will not do it for upto a month, then out of the blue it starts doing it again. I would realy like to find the problem but am at a loss as to what else it could be.
Phil

 

i am going to bypass the heater core and see if that stops the fluctuation. if so then the heater core is partially blocked and can not handle the high flow of coolant when engine rpms are up. i will post to inform you on my findings.

sam_animal, what type of truck/motor do you have this problem with?

i also noticed today that the volt meter bounces back and forth when i am at a red light. not alot, just a small amount. it also drops a little when i first hit the brakes but comes right back up. when i start the truck cold, in the morning, the volt meter shakes almost and the dash and head lights flicker for about 2 seconds. never noticed this before so i am wondering if this is part of the problem. is this normal and if not, could it have any effect on the temp, ie. the temp sesor for the computer changing how the egine is running.

thanks again.

 

this sounds to me like the vlotage stabilizer for the gauges is playing up, sorry but I have no clue were this would be on the f150.

 

An air pocket in the system will sometimes cause this to happen,but it is not a common problem on this truck.I had a 90 250 w/351 that did this same thing(all of a sudden) and it turned out to be heater core.So it won't hurt to try bypassing it.

 

I recently purchased a '95 f150 5.0L, AOD, with the exact same temperature fluctuation problem. I noticed it when I was buying it and thought it would be nothing more than a sending unit and a thermostat. Since I've tried a OEM thermostat, both coolant sending units(gauge & ECM), and a new radiator(which was leaking). PLEASE KEEP ME POSTED !!!!

 

this may sound dumb but... how are the hoses?? i know with my truck, the new lower rad. hose i have has a wire winding in it, its the same as the one on the f-350 i have at work, and its to keep the hose from colapsing when it is hot and the water pump is circulating, just for grins and gigles, get the truck to where it is HOT and look at the hoses, make sure they arent sucked togather restricting flow.

 

well tonight i replaced the radiator and water pump. NO LUCK. same thing i also flushed the heater core with a garden hose and i little bit of sediment came out, but nothing that would effect it at all.

only thing now is the tranny line started to leak on startup, created a puddle of tranny fluid in the botum of radiator support. fixed leak, but the fluid seems to keep getting sprayed around by the fan(i also soaked up the fluid that had already leaked.

the radiator looked pretty bad and the pump was only 30 bucks so im not too upset it didnt work but would really like to get to the bottum of this asap as i drive it 70 miles each day.

if it was a voltage regulator, wouldnt all of the gauges fluctuate not just the temp one.

thanks for the help, and ill keep you posted.

 

This is defiantly a big stumper....
The only part of the cooling system you did not address is in the engine its self...engine internal flow.
First a question, was the engine ever rebuilt? How long you own the truck?

I think head gaskets on this engine are not interchangeable left and right...it may block some cooling passage ways, if on wrong sides.
But....the big thing is this is a problem that started all of a sudden...so might not be the problem.

Another is scale or buildup...in the engine.
Did the old radiator have any build up?
I’m thinking some buildup, if there is any...let lose and is plugging up some passages, causing it to heat up when the engine is working hard creating heat, but not able to release it fast enough in the cooling system to cool down..
Did you back flush the engine itself?

I’m a tech at a ford dealership, so I’ll see if I can’t find some info for ya
Oh and I lived in Plymouth Wisconsin....but recently moved to Colorado.

Oh and put some thread tape on the Trans lines on the rad...But make sure no tape gets into the Trans lines....could be fatal to the Trans.
The fluid goes strait to the lubrication circuit in the transmission, from the cooler.

 

This was my first thought after reading through the list of what you had already done. Is it possible that a hose may be kinked? May be a combination of an air pocket and an old weak hose.

 

thank again every one.

madman, they old rad looked pretty clean inside and the pump looked almost mint, with just some very minor rust starting on the impeller. i am not exactly sure how to back flush the motor, but i did drain the rad, heater core, and block(left side only) filled up with water and cleande, ran and drove for about 40 mins, drained all again completely, replace rad and water pump. refilled, burped the system, came up to tmep pretty quick and stayed there for about 15 mins. then i drove it i noticed the temp increase is not instant. ie. when i give it a little more gas to accelerate or go up a hill, the gauge stays where it is and then about 10 secs later comes up but only for about 20-30 secs and then goes back down.

what really confuses me is that i used a sheet of cardboard to block the rad. on every other truck ive owned, if i let it idle like this for about 10 mins, the temp would go through the roof, but it did not heat up any more. this just further confused me. any thoughts.

thanks again for all the help. hopefully i get this figured out soon, it's driving me insane.

 

madman, i forgot to mention, i do not know if the engine has been rebuilt. i have owned the truck for about 2 years and put about 40k on it. never had any other problems with it as far as the cooling system. about a 2 months ago, the cat clogged up and actually melted when i was on the high way. replaced the cat and pass side exhst. manifold. but i do not think that would have anything to do with it, esp. since it was done over a month before this started happening

thanks again