My 1991 4.9L 5-speed has come close to overheating twice this week. I got home yesterday with the needle approaching the A in Normal- this truck usually runs (rolling) below the N. Parked it, popped the hood, and could hear coolant boiling in the reservoir. This truck's been doing very well for the past year with no prior heat issues, tends to run cold when rolling. Doesn't appear to be leaking or burning anything.

The water pump is working, I think the thermostat is either working or failed-open. The coolant is fairly new and around a 65/35 water/antifreeze mix. Oil is decent. Motor runs fine, A/C blows cold, fan clutch is OK. I think it's a combination of the retarded single-core radiator Ford shipped it with and my A/C add-in from last fall. Still, it heats up fast with or without the A/C on. Contact thermometer puts the temps at approximately 220-230 degrees at the upper coolant hose and 225 at the radiator cap, thermostat temperature was a 160 at installation, housing reads 230 to thermometer.

Aside from E-fans, what can I do to save this truck? I'm getting my 2008 F150 back next Saturday, so I'll have some downtime to tear into the '91.

As an aside, should I trade in the 2008 for a fuel-efficient ride? I've got the '91 for pretty much any normal truck stuff, and big moves = Uhaul anyways. It's a 2008 Supercab STX 4.6L with 76,000 miles on it, reckon it'd be around $9k at trade-in (about what I owe, more or less).

Worst-case, I've got two F150s. The '91 will never sell for what I want.

 

I'm not one to join the t-stat crowd, but your description of "heats up fast". Let that be your starting point. Don't worry about the single core radiator at this time, get the truck running right and go from there. How does the fan clutch feel? Should have slight resistance to it with engine off. I assume it still has a fan shroud.

 

A few things to consider: Radiator Cap, Thermostat (I prefer Stant Superstat) and as the previous poster mentioned, check to ensure the fan clutch has good resistance. The single core radiator should be ok. I have one on my V8 and it cooled fine once I replaced the fan clutch. Although a 3 core HD radiator would be nice!

 

If you still have the contact thermometer handy, check for cold spots in the radiator cores.

 

Like has been said, I'd suspect the thermostat first. My single core rad running with dual e fans takes a good 10 - 15 minutes to warm up at idle before the temp reaches 195 and the fans come on. I'm only running about 25% antifreeze if that. Driving down the road with 95 degree outside temps, the fans never turn on. I'd replace the thermostat with a 185 and flush the system. Refill with straight water for testing and see where your at. If that fixes it, drain the rad and put in a gallon of antifreeze and top it off. I bought radiator flush but wound up using dawn detergent and got allot more junk out of the system. Flushed the dawn with straight water for 30 minutes, added antifreeze and never looked back. I had an oilfield mechanic tell me about the dawn and was skeptical, but it worked great!

 

Bath beads also work great. Dump em in, let it run for 30 minutes, drain it and you're good.

 

Grab a new rad cap because its easiest , and cheap.

 

I have 'squeezed the top right hose (that goes to thermostat?) and there is nothing there! So I removed it to see if any fluid comes out and the answer is no. I did this as I thought the 'heated' fluid would cause the thermostat to open but since it gets 'no fluid' is it my water pump?