I have been having overheating problems at highway speeds (60mph) when temps are above 90 degrees. I can drive all day long with the a/c going in regular traffic and the temp is fine. When I jump on the highway and hold a steady speed @ 60 mph the temp creeps up sloooowwly to the L on the NORMAL gauge within about 10 miles, even if I pull over I cannot cool it down until I run water through the radiator, If I shut it off I wont be able to restart it untill the next day. I have been reading the 73-79 threads and this thread and tried everything. Let me tell you what it is I have and what I have done to this truck.
1978 F150 2wd
351m/400 with c-6 with 3.55 gears,32 inch bf goodrich AT's
The 351m was rebuilt about 3 years ago with a mild RV cam. Nothing special.
new stock distributor, MSD 6a box. MSD Blaster coil.
year old edelbrock intake with a 2-barrel 2150 and adaptor (no 4-barrel yet) no egr.
Brand new 460 radiator, custom shroud for it,
Running about 60% antifreeze
new fan clutch (changed twice),
new Water pump.
robertshaw thermostat 333-192. Also tried the Mr Gasket brand.
Flushed the engine when the water pump was out( not clogged)
Ran the engine with no thermostat to see the water running in the radiator. Tested the thermostat (All of them),
Pressure tested the radiator (no head gasket leak),
My timing is set at 14 btdc initial with about 35 btdc at 2300 rpm
I have also tried both intake vacuum and spark vacuum.
The truck runs at about 2350 rpm at 60 mph and shoots up quickly if i go any faster.
This truck always starts on the first try, idles beautifully, has great power, and I love wrenching on her but this is driving me nuts. AAAAAAAAAny Ideas ?? Thanks in advance. firefdude


I also have true dual exhaust with two turbo mufflers.(sounds nice)

 

do you know if the advance continues to climb from your 2300 rpm reference point? how many degrees does it total out at and at what rpm?

could be going lean.

 

My total advance maxes out at about 35 btdc at 2300rpm. Do you think its time to step up to the 4 barrel? The 2150 is a 300cfm.

 

FRICTION!!!

The motor has excess friction, and at higher RPM, it can't get rid of the heat fast enough.

When you shut it off, and can't restart, it's because the bearings are overheated.

How is your oil pressure? At Idle? While Running?

Does your oil pressure drop after running at 60 MPH for a while?

What oil do you use?

 

limited cfm alone can't be a problem, the carby should be mixing the correct amount of fuel to the air being drawn through it. even if the engine wants more air/fuel mix, the limited mix should still be at the correct ratio. i'd move on to the 4bbl rather than sort out the 2bbl, if that's your ultimate plan anyway.

friction? better get castrol gtx before your engine does something to get you heated up!

 

It might be the clutch fan.

 

even tho you can "see" water circulating in the rad it might be half pluged. this is the reason i do not use silicone on water pumps,t-stat ect. either take the rad to a shop and have it roded out(boiling wont get out silicone) or just find a different one.

 

I use castrol gtx 10w30 and my oil pressure starts high until it warms up and stays at the halfway mark no matter how hot it gets (even when overheating)
As far as the fan clutch goes, Ive replaced it twice and it does engage when temp rises. The new radiator gets hot uniformly, I have a temperature gun with laser pointer, if It was clogged I would have gotten uneven temps. Oh and as far as the not starting, I took my starter out and had it tested yesterday, it was bad. replaced it and all is fine for now. Any other ideas?????? Please.

 

What about the collapsing coolant hose problem where the lower hose is weak from age and closes itself off when the flow rate is highest?

 

I went and bought an 1 3/4" diameter stainless "slinky" looking wire and inserted it in the lower hose. about 4 bucks a foot.

 

Slipping fan belt? An old belt can slip and not make noise.

 

Faulty guage/sensor?


ACG

 

What shoots up faster, temp or RPM?

 

This article is so you, dude:

http://www.yarchive.net/car/radiator_diagnosis.html

Let me know if you catch a fish.

GL

 

I meant the rpm goes up.
ECURI.....good link I'll try a couple of things. when overheating, the temperatures are the same at both the top and bottom hoses.
I'm leaning more toward the air restriction theory since the new radiator is about 6-8 inches taller (the extra height is actually on the bottom) and that is where the front bumper blocks the air flow. A soon as I get some time I'm gonna take the front bumper off and jump on the highway to see if this is my problem. I'll keep all of you posted.