getting hot

[Austin86250]

alright i got an interesting over heating problem on a 88 f350 7.3 its got me stumped so hopefully someone who is smarter than me can shed some light

so truck does amazing under 2500 rpm stays right in the normal operating temp never things about getting hot
but when you get above 2500 (cruzing speed is about 2700 at 70 which is most of the roads round here) within 5 seconds it goes right to "al" and sometimes a little past "L" and when you bring it back down to about 2300 or lower she goes right back to operating temp

temp sensor brand new

coolant is great still green and i checked it with those little meters and it says its good for minus 30 and its got SCA added as well as royal purple cooling additive

fan clutch is nice and tight

im guessing its not thermostat related as i havent seen a bad thermostat create these specific issues

water pump is not leaking, is it possible for the weep hole to be clogged?

my only real guess is the rad, its not leaking but perhaps it could be clogged?

thanks for reading!

 

[Jesus Freak]

It could be the radiator, but is it REALLY getting hot. The 30+ yr old factory temp gauge could be wonky.

 

[SkylabTech86IDI]

You should verify with a laser temp gun how hot it is getting.

Also, make sure your radiator cap is nice and tight and that it holds the proper seal.

 

[Austin86250]

It could be the radiator, but is it REALLY getting hot. The 30+ yr old factory temp gauge could be wonky.

I dont know how hot but it’s defiantly getting hot whips of smoke from rad/ overflow tank

 

[Austin86250]

You should verify with a laser temp gun how hot it is getting.

Also, make sure your radiator cap is nice and tight and that it holds the proper seal.

Ah good call completely forgot about the cap!

 

[IDIBRONCO]

It could be the radiator, but is it REALLY getting hot. The 30+ yr old factory temp gauge could be wonky.

It's the gauge. It's impossible for your engine to heat up that quickly and then cool back down that quickly just from RPM. The only way that your gauge would be correctly showing your engine heating up that quickly is if you had a bad head gasket or a cracked head. You do not have the symptoms of those so you don't have that issue.
The moral of the story? Put a quality set of aftermarket gauges in your truck if you want reliable readings.

Ah good call completely forgot about the cap!

Yes Skylab nailed that one.

 

[Austin86250]

It's the gauge. It's impossible for your engine to heat up that quickly and then cool back down that quickly just from RPM. The only way that your gauge would be correctly showing your engine heating up that quickly is if you had a bad head gasket or a cracked head. You do not have the symptoms of those so you don't have that issue.
The moral of the story? Put a quality set of aftermarket gauges in your truck if you want reliable readings.

Yes Skylab nailed that one.

You do make a great point, I’ll go find one and see how hot I’m really getting I know it’s above operating temp though

 

[Jesus Freak]

It's the gauge. It's impossible for your engine to heat up that quickly and then cool back down that quickly just from RPM. The only way that your gauge would be correctly showing your engine heating up that quickly is if you had a bad head gasket or a cracked head. You do not have the symptoms of those so you don't have that issue.
The moral of the story? Put a quality set of aftermarket gauges in your truck if you want reliable readings.

Yes Skylab nailed that one.

That was my theory.

 

[IDIBRONCO]

I know it’s above operating temp though

How do you know? Your factory gauge moves quickly. Explain how your coolant temperature can heat up that quickly and then cool back off that quickly. Even a plugged radiator can't make the engine heat up that much, in 5 seconds, just by raising the RPM by 200. That's practically instantly. A plugged radiator can make the coolant temp rise like that, but not in 5 seconds. It also won't let the coolant temp drop that quickly. It would take a lot more time than that.

 

[IDIBRONCO]

How do you know? Your factory gauge moves quickly. Explain how your coolant temperature can heat up that quickly and then cool back off that quickly. Even a plugged radiator can't make the engine heat up that much, in 5 seconds, just by raising the RPM by 200. That's practically instantly. A plugged radiator can make the coolant temp rise like that, but not in 5 seconds. It also won't let the coolant temp drop that quickly. It would take a lot more time than that.

Of course my next question would be what is your engine's operating temperature? Then how do you know what it is?

 

[IDIBRONCO]

That was my theory.

It's not a theory. It's fact.

 

[Austin86250]

im relaying the info ive gotten form my buddy as he is on a road trip, you are right that does not make since for it to change that rapidly ill have him go buy a heat gun

 

[franklin2]

Does your little engine light on the dash come on at the same time? If it does, it could be the overheat switch. These trucks have two sensors, one runs the gauge and the other is a switch that when it gets to a certain temp, the switch pegs the gauge and turns the dash light on. One of Fords better ideas.

Get a real gauge like the others said.

If it still does it, the only other thing I can think of that would cause it to overheat at a high rpm would be the lower radiator hose is collapsing. It should have a metal spring in the hose. If it doesn't, the waterpump can collapse the hose at high rpm when the hose gets soft.

 

[Austin86250]

Does your little engine light on the dash come on at the same time? If it does, it could be the overheat switch. These trucks have two sensors, one runs the gauge and the other is a switch that when it gets to a certain temp, the switch pegs the gauge and turns the dash light on. One of Fords better ideas.

Get a real gauge like the others said.

If it still does it, the only other thing I can think of that would cause it to overheat at a high rpm would be the lower radiator hose is collapsing. It should have a metal spring in the hose. If it doesn't, the waterpump can collapse the hose at high rpm when the hose gets soft.

the temp switch has been disconnected as it just pegged the gauge out all the time

 

[03wr250f]

Put a real gauge on it and go from there, the factory gauge is incredibly inaccurate .
Put a stant rad cap on it from napa(house brand is stant)
And is the fan clutch locking ever? If not likely bad.
First place is still a real gauge