As long as I have owned this '96 I6 truck the temp gauge has never even broke the plane of the "N". A few days ago I noticed a radiator leak, and the temp gauge rose a little. I went ahead and replaced the radiator, upper and lower hoses, hose to the overflow tank, new cap, clamps, etc. Flushed the system and replaced with new 50/50 premixed coolant. Pretty standard. Now the truck rides with the needle right between the "N" and the "O", I first took it on the road/highway for about a 45 minute drive since the repair.

Parked it and after a few minutes the radiator cap pops off and blows some steam. I am almost positive the cap was on all the way and correct. Could there be too much coolant? Just nervous becuase I have a big drive tomorrow. Thanks for your help.

 

Another thought was maybe an air pocket from the fluid exchange would cause something like that? Faulty radiator cap even though it was new?

 

When your truck is cold try "massaging" the big upper hose as you fill the rad from the top cap. Once your fluid is almost at the top of the cap and your reservoir is at the cold fill line, massage the hose (seriously guys, come on) until bubbles come out from the top.


You'll be surprised how many times you have to do this. Once it seems totally full put the cap back on (through away that junk cap and get yourself a good 12$ cap at a parts store that has a pressure bleeder leaver on the top) compress the hose again and it should get rid of any air in the small line that goes to your reservoir (you'll hear it burp).


If that doesn't work, then probably have a cracked rad. I replaced mine recently and the hose lines pressure up nicely while its hot, as it should be.

 

So basically air pockets caused the cap to blow off like that after the truck had turned off. I hope the radiator isn't cracked becuase its brand new, and I did replace the old cap with one that has that red safety lever on top.

 

Radiator caps don't pop off. You probably didn't have it on all the way. They're designed to lock.
Get all the air out by getting it hot and letting it cool right down a few times.
The big valve in the cap lets pressure out when it gets to about 15 psi (or whatever the cap is designed for) and the tiny one in the center allows the motor to suck fluid back as it cools and contracts.
Take a jug of premixed coolant (50/50 with water) with you in case you have a problem on the road.

 

This this popped off pretty violently too. If it wasn't on all the way wouldn't it have just popped off while I was driving, esp at highway speeds and a warm engine? Good call on the other techniques though, I will try them tomorrow.

 

Oh also any thoughts on the new "normal" reading on the temp gauge?

 

I've fixed a bunch f150's with this issue, including mine. When I got my 95 last year the temp gauge read read right on the O and would fluctuate very little. However, the truck overheated on me on my way home from work. The gauge would read, but read wrong.

Pull the sensor out and connect it back to the wire. Get a thermometer and boil some water in a pan. When it gets to 212 and boiling take the pan outside and dip the sending unit in it. Then get in, turn the key on, and see where the gauge reads. I'd bet money you have a bad sending unit.

Or, if you don't want to do all that, the sensor only costs about $12.

 

This is gonna be a touchy suubject but check your clutch fan I changed thermostat radiator hoses and thought my clutch fan was good took it to auto parts store to compare with a new one and only felt a slight difference and after a few min said what the hell bought it and what a difference it made. My truck on start up sounds like a dump truck now lol I hear that clutch fan working. These vehicles need a proper working cooling system with there little radiators. Any part of the cooling system that has a week point is critical because of the small radiator. The new clutch fan was 64 bucs and well worth every penny I upgraded to a newradiator also 130 bucs auto zone and 160 thermostat the radiator was 1inch and new radiator was 2 and quarter or half something like that. The clutch fan was all the difference and needs to pull that air weather you have a 1 or 2 inch radiator you could have a 100 gallon radiotor lol and if no air is pulled over it its notgonna cool the water good luckmy friend

 

That could also be a faulty rad cap too. They're designed to pressurize the coolant a little as that raises the boiling point (keeping the coolant from turning to steam at normal boiling point).
It should release pressure at 12 to 15 psi out to the overflow. As the engine cools and the coolant contracts, it can draw back from the overflow.
If it doesn't release pressure it will just keep building.
You should be able to compress that large spring part with your thumbs fairly easily (12 - 15 lbs). If it's really really hard to do that's a problem.
You should be able to pull the little button in the center out a little really easily - that's how it draws fluid back into the engine.
Best thing is to buy a top brand rad cap and never mind the gimmicks like that pressure release thing. That's just something that's totally unnecessary in day to day normal operation.
Keep the overflow bottle topped up to the line and the cooling system will manage itself.