[85f150]

this is driving me nuts...I put a new t stat in a couple of months back because the housing was leaking so i figured why not. about 3 weeks ago it started running on the l on the normal side of the gauge. So this weekend i replaced the new radiator of my 88 and put it in this 85 (both have 4.9's). Filled it up and cruized down the road. Now my temp gauge is pegged on the aftermarket and fact. So i had my dad pick up a new t-stat just in case. R&R still didn't help any. When i was removing it i blew with ease into the top rad hose and the coolant came out the head no probs. This time when i came home i popped the hood and checked the hoses. Top one into rad is warm, can hold hand on for about 5-10 secs, bottom one is warm but not as hot as top. Heater hoses are same heat level as top rad. Both temp gauges are hooked up in the only possible place, right below exhaust manifold in the back passenger side of the head. I tried the aftermarket gauge where the ECT goes but it will only read 100F and nothing higher.....SO the fact gauge is pegged, and the aftermarket says it is about 300F....which is not possible because the damn block would be split open and there is no way that heater/rad hoses would be that cool. .....could this be a possible ground prob...which i can't beleive because it doesn't happen until it is warmed up doing 45mph or higher, in town it drops to about 190...i am just totally lost here....what the heck could of happened...i am thinking of going to my uncles because he has the little laser temp measurer and checking it out...there is just no way it could be running that hot though and no freaking steam.... :boxing :boxing :boxing :boxing :boxing :twak :twak :twak :twak


thanks for any suggestions guys/galz

 

[Blaze]

Stopped up rad.?? :shrug

 

[84brownbronco]

all i know is when i thought mine was overheating it was just the factory gauge messing up. but you already have a aftermarket temp gauge so that cant be it.

 

[84brownbronco]

oh also there sometimes can be a air pocket in the system and can overheat. my dads Trans Am did that. got air and it would randomly overheat.

 

[85f150]

i thought about the air pockets too...but like i was saying before the block is definatly not that warm....no way is it 300 degrees farenheit....that is why i am totally confused....well i am tearing my 351 down tomorrow to i can hurry up and get it in...but i would like to solve this...

 

[Ironclad]

If you've got variants in the temp between highway and in town cruising then the gauge is probably functioning? I'd check the connections anyhow, but try installing a lower temp thermostat. Since this just happened since you installed a new one, that'd be the first thing I would suspect.

Also.... just because you can blow water out of the block does not mean you have good flow. Bad problem on older high mile engines. Especially if you don't know the history of the engine? If there's ever been a leak, someone kept pouring in block/radiator sealer either until it worked or they had to fix the problem.

I recently tore apart an 88 302 that was all gunked up inside the water ports. It also had overheating issues. Excessive high temps on the gauge, but no steam, no blown hoses etc. If this is an older high mileage engine, you might also consider flushing that rascal out.

 

[85f150]

i replaced the t stat 2 months ago and just replaced it sunday both were 195 i think...on the rad...i just flushed it this summer 2 long times...so i know it isn't plugged....the wire was melted on the stock gauge so i put a new connector and also installed my aft mrkt gauge there...this didn't start just after the recent new t stat it has said it was running on the l of normal for about three weeks, that is why i decided to R&R the rad....now it is just saying it is running warmer...

 

[Spade]

Is there any update to this thread? I am having the same problem. Intown temp is great, on the hwy 55 or up for more than 15 min temp guage goes straight up. Before this happened I replaced a leaky water pump, thermostat and all hoses. I never had an over heating problem before replacing the water pump and t-stat. I have replaced the t-stat and temp sending unit since and still have the same problem. There is no play in the water pump pulley(with belt removed) have checked several times for air pockets. I was thinking about changing the t-stat to a lower one but I don't want to keep throwing parts at it. Is it possible the pump is just not pumping enough at high speeds?

Also I have flushed radiator. Thanks.

 

[jermil01]

Having just dealt with this problem, I replaced my radiator, and added a new heavy duty fan clutch. Before all of this mine was running well above the normal range, that was with the 195 degree 'stat. I switched to the lower 160 degree 'stat, but I have a feeling that is too low, my temp gauge now barely gets up to N in NORMAL, I'm going to run a 180. I'm thinking there is most likely something wrong with the gague which isn't unimaginable, but could a clogged or heater core that is about to go also cause this? I don't know.

 

[JDApollo]

I've never seen a waterpump fail as in it no longer pumped enough fluid. It has always been the water pump leaks, or the bearings fail and you know that right away when the pulley comes off while your going down the road. I mean if you look at how a water pump is built whats to go wrong if it spins then the impeller will move water. I learned the fan on my 85 was designed to be rotated clockwise and when I put the 93 engine in it and the 85 fan on the serpentine belt pully that it wasn't doing me any goodcause the serpentine belt drives the fan (and water pump) from the back side of the belt and thus it rotates counter clockwise. So if you changed water pumps and some how got a pump designed to go in hte opposite direction than what your spinning it. I think that could be a problem. As for a temp. reading of 300* i would check to see if the probe was touching the casting some how inside the water jacket. The probe needs to be in a region of the water jacket that gets good flow. Also using the infared temp. gun to daignose the problem is a good idea. I use mine for that kind of thing all the time

 

[Spade]

I should not have said "the same problem" but very close.

I read that at high speeds the hoses can be sucked shut. Well this got me thinking, and I could be way off but... When I installed my new bottom hose it was shaped slightly different than my o.e. and it almost has a flat spot(oblong instead of round.) I wonder if that might be my problem?

 

[The Yak]

If it's a high mileage motor, it's possible that the water jackets are partially blocked with shiz, thus not allowing sufficient flow back to the radiator.

Try a 160* thermostat.

 

[85f150]

no real updates, i replaced water pump because it started leaking around the shaft, then my rad started leaking at the top row (shitty manufacturing) so i replaced it with one from a a/c equiped wich gave me another row....ow i can cruise 55mph at normal temps but s soon as i get bave that both my temp gauges peg. What ws even neater was during hte winter i could cruise 70mph with the plow on and the truck would barely even warm up :shrug i think mine may have something also to do with the leaky exhaust mainfold gasket (both happened about the same time), the temp sending unit and aft gauge are right below the exhaust manifold on the 4.9, i will find out if that is the prob this summer when i put efi manifold on and run new exhaust