I tried this in the heating forum already, I guess I will try it here. Thanks Steve for the reply, but I swapped the gauge and that didn't help.

Here is the situation:

I found a small leak on my themostat housing gasket so I replaced the gasket and refilled my coolant. Ran the truck, checked for air. A day or two after changing the gasket, I was watching the temp gauge. It was doing the exact same thing that 88Bronc posted in the "getting hot" post (https://www.ford-trucks.com/dcforum/DCForumID39/6832.html).

My truck normally runs around the "N" to the "O" in NORMAL. Lately it will warm up and stay there at idle. As soon as I start moving it will start to warm up, rapidly. It will go past the "L" and then slowly fall back to below the "N". When it is running hot, if I step on the gas or rev it up the temp will go back down quickly. I run an electric fan, that is thermostatically controlled, and it never kicks on when the temp gets up that high. I know the fan works, I know the coolant is full and I am pretty sure there is no air in the system. I have replaced the radiator cap and I am going to try the temp sending unit this afternoon, anyone have any other ideas? It doesn't seem to be hurting anything, just driving me nuts. I don't see any leaks anywhere, but if there is a leak, could that be my problem? I am thinking that after fixing the therm gasket, I may have blown another gasket somewhere else. I hear that the intake manifold gaskets like to blow in the back of the 351w.

 

[updated:LAST EDITED ON 30-Dec-02 AT 10:08 AM (EST)]Did you verify that the coolant level is full? If the t-stat isn't open the rad will be full giving the impression that it is full. I usually run it for 20-30 minutes with the cap off and squeeze the upper and lower hoses to "burp" the air out. When the t-stat opens it will suck the rad dry, so be prepared to fill it up. You'd be amazed how much air can be in there.
Also, did you change the t-stat while you changed the gasket?

Keep us posted.

John

 

Also, Swirk,

How hard was it to do the 6 to 351W swap? Is it mass-air? I've been thinking about this for a while.

John

 

Apparently the swap from 6 to 351 is easier than changing my thermostat gasket. Haha.

I didn't replace the thermostat because it was only 6 months old, but it is one of my next moves. I have run the truck until warm, shut it off, and opened the rad cap, then turned the truck on again and waited for it go down, and refilled it. I did notice two things with the rad cap off, first if you rev the motor with the cap off, the coolant level goes way down and when you stop revving, it flows out the top of the radiator. Second, if I put my hand over the top of the radiator and rev the motor, there is quite a bit of suction under my hand. I think that this is how it should work, but it seems funny.

As far as the engine swap. It took me most of a weekend to swap the motors. Fairly easy, just time consuming. The 351 is a BIG improvement over the 6. I would suggest doing your homework and asking questions if you are not sure (I research it for about 6 months before I swapped my motors). The swap did cost me a little more than $1500 including the motor (after I sold the 6). I got my motor from a junkyard with 62K miles on it. With a radiator, it cost me $850. That included the complete motor (wiring harness & fuel injection) and radiator. After that I did basic tune up, replaced most of the gaskets and seals, and had a little head work done (ported and polished, new valves). I also put headers, a dual exhaust, and a couple of other go fast goodies on the motor before the swap. You have to buy a computer, because the fuel injection is controlled by the computer. Some of the accessories will swap over (power sterring pump, A/C, smog pump) but the alternator is different. You will have to buy the V8 hoses - radiator, A/C, and power steering. The air filter box is the same. Mine is a standard, I don't think they put mass air on a 5 speed 351. I think they did on the 302s in 96, but I am not sure. So, mine is speed density. If you have an older truck and swap the motor AND want Mass Air, you could just get the computer for the right motor/tranny application. Automatics have Mass Air ('94 and up) and 5 speeds don't. The only pain was swapping the frame mounts. There are two, left and right. The driver's side is riveted on, you need to get the rivets out to bolt the new mount in. That took me 2 hours+. The one thing that made the whole swap easier, was that I have a 3" body lift on the truck. That helped a lot.

I enjoyed the swap, it was a good experience. I would do it again.

 

My truck did the same thing. It was just the thermostat going bad. Just put a new one in and it'll fix it.

Dan

'95 F150 Eddie B
Heavy Duty Springs
32 BFG AT KOs
3.73's w/ trac loc rear
smittybilt push bar w/ 2 KCs
clearance lights and custom fogs
System One racking
"A mean work truck"

 

 

Your running too hot of a thermostat. You most likely have a 195* thermo in there. Go ahead and buy the 160* thermostat! That's what I did to my 90 Bronco with a 351W now it never go's past the "N" on the gauge!!

 

195 shouldn't be too hot; Ford designed these engines to run at this temperature. If you run a thermostat too cool your truck will never warm up to its proper operating temperature and will always run rich.

--------------
1995 F-150 Supercab XLT 155" 4x4 M5OD 302
1986 F-150 4x4 NP435 300

 

190-195 is the proper temp for that motor. Unless you tow, I don't see the need for a 160. just replace it with a fail safe one.

Dan

'95 F150 Eddie B
Heavy Duty Springs
32 BFG AT KOs
3.73's w/ trac loc rear
smittybilt push bar w/ 2 KCs
clearance lights and custom fogs
System One racking
"A mean work truck"

 

It could be a bad T-stat. When I replaced mine I drilled a small hole in the rim so as no to be affected by the gasket and installed the T-stat with the hole at the uppermost position. This helps the air trapped in the system bleed out. Fords are bad this way. Some T-stats come this way from the factory and a fail-safe sts is a good way to go if you can find one. If they go bad they open in stead of staying closed. Another thing to check is the bottom rad hose. It may be colapsing under water pump load at speed. The reinforcing spring inside the hose may have rusted out causing the hose to flatten when the engine is running fast and the water pump is sucking hard on the hose. I have had this happen but on a n old Chrysler M300. I replaced and flushed everything except that bottom hose and it was the culprit. Oh well, a lesson well learned.
Happy New Year Y'all.

 

It was the thermostat. I replaced it and everything is fine.
Thanks guys!!