Here is some things to coinsider that I have learned about engine cooling:

Fan Clutches: There are two different styles on the market; thermal and non-thermal. Thermal will engage tighter when the air being pulled through the radiator reaches a certain temperature; however, they will never engage 100% due to some hydraulic slippage. Non-thermal clutches remain in a halfway engaged position no matter what the temp. This is fine at an idle, but it does not pull much at higher RPM. As someone else said, bumping the RPM up to 1500-2000 for a minute or so will often cool-down an engine, but probably not as well, if any, with a non-thermal clutch or a flex-fan. You can easily tell the two clutches apart. A thermal style will have a coil attached to the front of it, similar to those large outdoor dial-style themometers. However, no clutch is going to pull more air than your direct-drive, fixed-pitch fan. The best you could do here would be to get a bigger fan. 16 inch seems small. Most pickup fans I have seen measure 18-19 inches.

Electric Fans: Not sure why, but I have always heard that these are more effective as a puller (between radiator & engine) rather than a pusher (between grill & radiator).

Radiators: Aluminum is more efficient than brass/copper. A 2-row aluminum can actually out-cool a 4-row brass/copper. This is because the aluminum tubes can be made out of thinner material(less insulating) and larger (more surface area) without balloning/bursting from pressure.

Here is a trick that some RVers (motorhomes) have done for travel in extreme climates. They hooked up a winshield washer pump to their fresh water tank to spray a fine mist in front of their radiator using several tiny jets. When the temperature gets too high, they just turn the pump on for a few seconds. Seems crude, but I would have to believe it is highly effective since water dissapates heat from metal many times better that air does.

Fan Shroud: Yes. Also required for safety sake. Touch the back of a spinning fan and it gives you a slap; touch the front and you will never touch it again (at least with the same hand).

 

We definitely had some more food for thought here while I was out trying not to think about cooling. I made an error earlier in the fan blade dimension. I checked my notes and it IS an 18-incher, but there may be room for a larger one, depending on the fan shroud Iwhich should arrive in a few days). If the shroud doesn't solve the problem, I'll have to look at fan alternatives. My impression of the flex-fans was that they had a deep scoop at low rpms, for higher low-engine-speed airflow -- which sounds like something that might help me.

The high-perf stat with the bigger hole is interesting, but that might afect the system much like when I had no thermostat and the engine temp went through the roof compared to either a 180 or 195. Imay try a 160, though, when I install the shroud. I'm not sure whether either type of clutch fan would improve the low-rpm cooling where the real problem is.

I also have a 302 in a '78 window van that has never had a cooling problem, even in 3-hour summer traffic jams with the air on. This is my first such problem with any Ford.

The RV "spray" trick is clever, and should work well. Since this truck also carries a 275-gallon fresh water tank, I may rig up something just for emergencies until this gets sorted out permanently. I have high hopes that the shroud may make a real difference shortly.

It now occurs to me that I should take a very careful look at the fan belt, also. It's not likely that it's the problem, or that five or six of us missed something that basic, but stranger things have happened. I'm going to try the water wetter, also. My order of attack then should be: fan shroud, and then a larger, or alternate type, of fan. The description of the theory behind shroud and fan design was a real education and I'm going to stick to that design as closely as possible. Many thanks for the excellent insights & ideas.

Gid

 

Fan belt was OK. Today it ran close to 230 during the route since there were more stops, closer together. I picked up a bottle of "water wetter" and will stick it in before tomorrow's run to compare temps. I want to give a big plug for autokrafters.com, from whom I ordered the fan shroud yesterday morning. They went the extra mile in pulling the shroud off the shelf for me and giving me very careful measurements over the phone to see if it might fit this truck. When I ordered it yesterday, they mentioned that they were running a day or so behind in getting orders filled, but they'd try to expedite this one since they knew I had an overheating problem. Well, the shroud arrived this morning, less than 24 hours after I spoke to them. I'm really impressed with this group.

We'll probably have to do some significant modification, since the fan opening does appear to be much more off-center than fan, so we probably can't install it before Saturday or Sunday. Aside from the modifications, it looks pretty easy -- just removing the fan and maybe one or both of the radiator hoses, and then reinstalling the fan while the shroud is pushed back around the water pump. Probably one of those 20-minute jobs that stretch to four hours because of fitting, re-fitting, headscratching and trying to invent adapters and spacers out of beer cans and duct tape.

I'll report back about the water wetter tomorrow evening. According to the directions, it can be used with antifreeze, though the more dilute the mix, the better it works. The two people I've found who used it with 50/50 got an 8-10 degree reduction.

Gid

 

Gid,
Though I'd mention that the fans a suppose to enter the shroud only about 3/4 to one inch or so, or visa versa. I once had a problem in that I had a Holley "clean air" 600 on a 390Gt Ranchero running in the Central Valley in Ca. with temps are over 100 alot, It didn't like the carb, changed to a 750 vaccum along with a overflow tank ended the 230 temps forever after. Is it the same carb as was on the 351m? When they set the timing, you use to have to pull and plug the vaccum line to get it set right....
Jim

 

UPDATE: I was unsuccessful in getting a shroud installed and will have to try it next Saturday. Fortunately, the weather is supposed to be much cooler this week -- 60's & 70's. I could have hacked away at the new shroud and made something hastily, but now I think I have a design for some adjustable brackets so I won't have to make any drastic cuts I'd regret later.

My theory is that I should leave the fan cutout alone and simply adjust the shroud to sit in that spot with brackets, even though the shroud-to-radiator fit is off about an inch and a half or more. It hangs past the edge of the radiator on one side (and therefore must be blocked to force air thru the cores) and falls that much short on the other side. The hose cutouts are way off & will have to be patched & re-cut, too. Just in case any of you have the misfortune to tackle one like this, you probably need, like me, to make allowances for the edge of the radiator that the shroud flange blocks on the engine side. To keep out crud and insects that would eventually block the fins, I'll try to fit a fine-mesh screen over that strip. The only two other difficulty I can see is that two of the brackets probably should not actually contact the radiator fins (as they would since the 4-core is just as thick as the tanks) and the thin space they'll have to be offset will need to be filled with weatherstrip or something to make the air flow correct. I'll actually try to add something to the flange there so that air is pulled through every square inch of fins, but I doubt that'll work. However, if I have to settle for 90% flow thru a four-core and a shroud, that should be enough.

30 years ago, when I was young & foolish, I spent the summer stuffing a 413 wedge with long rams into a little Plymouth, and now I remember why I never did anything that radical again.

Gid

 

I can make cooling system diagnostics real simple for you.

Most people tend to over analyze the cooling system, and forget the simple physics involved.

A: If the engine runs hot at idle and very slow speeds, But runs at normal temp at highway speeds. The problem is airflow through the raidiator.

B: If it runs normal at idle or slow speeds, but runs hot at higher speeds. The problem is water flow. (And yes! to much is just as bad as not enough! i.e. no thermostat)

Using these simple, but absolute, rules, your problem is ...airflow through the raidiator (actualy a lack of airflow) So you need one or more of the following. Larger fan, more fan blades, ducting to control airflow (shroud) or move the fan closer to the radiator.

If it was me, I would put on a 7 or 8 blade fan (off of a Lincoln or Camper special or?) No fan clutch (unless you do a lot of highway driving and gas milage is a consideration)(A GOOD flex fan is an acceptable compromise, not a cheap one). And most importantly, a fan shroud! For this, you can take your truck to a heating/air conditioning sheat metal shop and they will take mesurments and make you an amazingly nice shroud! I had one made and it cost me $75.00. The best investment I ever made.

As a note to everyone else, If both A & B apply. (it runs hot at idle slow or crusing speeds) There is a malfunction in the system such as bad thermostat, bad fan clutch, blocked water passages, pluged radiator retarded timing etc.

 

I believe you're absolutely right that airflow is the main problem. It still puzzles me as to why with all the extreme measures I've taken so far (added electric fan, new giant-sized radiator) the problem, which never existed until the new engine went in, has just been slightly reduced. A couple of local mechanics have been kicking this around in their spare time and want to take a quick look at it this week and run a sniffer on it to see just exactly how lean it's running before we do a carb. Their tentative guess also is that a better fan is the next step after (or along with) the shroud. I tried two A/C sheet metal shops today and neither are interested in trying to make a shroud, but I have a couple of other ones to call. I'd rather have someone else do the aggravating fabrication work, but if all else fails I'll be under the truck Saturday a.m. -- I already have the adapter brackets mostly ready. If I do get a sheet metal shroud made, I'd better chain down the engine in case a motor mount goes again (one of Ford's nastier habits I've found). Otherwise the metal shrapnel could do some serious damage to radiator, fan, belts, hoses, etc., when the engine rises up.

Also, now we know where "too hot" is -- today it hit 240 at one long idle (15 min. in only 70-degree weather), and at that point it began to stagger when he got back in and hit the gas pedal.
-- Gid

 

Smokehill,
The only other thing that I've run into that did this was a cracked head. I'm not sure if anybody's mention this, but just to get it out on the table for thought. They can do a pressure check on the cooling system thats like a leak down test to see how it's holding pressure, and with the temps you've been seeing a radiator shop should be able to add some ideas. Hope I'm not just repeating things here.
Jim

 

UPDATE: The shroud is installed. My measurements were obviously flawed, since it fit perfectly, even on the oversized radiator. The only problem was overtightening the mounting bolts and cracking the plastic flange (not hard to fix). I cheated a bit & used nylon wire ties for the lower bolts. A word of caution (silly as it sounds): after I pressed the fan back in place to check the shroud fit & clearances, I nearly forgot to go back and reinstall the fan bolts -- very scary.

Jim, the leak-down test is a good idea & we'll do one later this week. It uses no coolant at all, though, so I don't expect to see a leak.

Will report back after we try this out.
Gid

 

 

UPDATE: The shroud seems to have helped more than anything else so far. The last two days have been rather cool (60's) with a fair amount of drizzle, so we can't be sure that all will be well when it gets back up to the 90's. It's staying around 180-190, going up to 210 at the absolute worst part of the route (an hour and a half in one construction project, mostly 15-minute idles with only short drives in between). Thanks to everyone on this Forum, we still have a few tricks up our sleeve even if this isn't the total solution. I think we'll add a hi-performance fan anyway, but only after we see how this setup works in hotter weather. My thanks for all the help and education -- will keep the Forum posted as we progress.
Gid