Hey there guys I have a friend that is having problems keeping his truck cool. As I stated it's a 86 f350 400 or 351m, 4 speed, 2wd. He has replaced the radiator, water pump, thermostat. I told him maybe the coolant is to rich maybe. It does fine idling it goes up to about 225 degrees under a load pulling a gooseneck trailer. Any ideas? He's not losing coolant. Doesn't mean it's not sucking air. Bit wanted your guys opinion.

 

I wonder if he has all the factory pieces to make that engine fit. Like the proper fan shroud, the proper radiator, the proper fan for that engine. The 351m/400 was not offered in 86, so someone put it in there, I would look it over carefully for something that would affect the cooling. Get online and look up a 81 or 82 with a 400 and see what type of radiator it took, and then see what he bought to put in it. They may have guessed and put a 351w radiator in it, I wonder if it is the same size radiator?

 

Yano actually you saying that reminded me it was an 81. Cause I remember telling him bout the Swiss cheese frame.. my bad. Memory bout as long as my pecker 😅😂

 

I would still make sure he has a fan shroud on it. If it has A/C, I would make sure the coil in front of the radiator is not full of bugs and dirt, even if the A/C does not work anymore.

Does it have a fan clutch? Is that kicking in? Usually if they work, it will kick in loudly each time he starts it in the morning for about 15 seconds or so, and then quiet down. If it doesn't do that, it is suspect.

 

The 351m/400 take their own thermostat. Plenty of examples of parts stores selling a Windsor stat even if you specify 351M. Worth confirming, and plenty of ‘net info on what it should be.

Good luck.

 

Does the truck have an aftermarket temperature gauge? If so, mechanical or electric? I ask because the stock gauge nomenclature only showed C-NORMAL-H.

Before your friend loads additional expensive items into the parts catapult (Pull!), it may be worthwhile to determine if you've got an actual overtemp situation or just a false indication.

Don't scoff at the possibility of an indication error. Many years ago, I had a car where the temp gauge would rapidly climb anytime I worked the engine hard. After much professional grade headscratching, a shop determined it was a bad gauge. The needle was accurate almost all of the time, until the coolant temp warmed near the upper end of the normal range. Above this magic number, the gauge erroneously showed much higher than the actual coolant temperature.

I'd strongly suggest springing for an infrared thermometer. You can get a decent example for only $20 or so. Duplicate the high temperature and pull over as quickly as possible and shut off the engine. Take a temperature reading at the thermostat housing and compare it to the dash gauge.

If not accurate, troubleshoot the indication system. If accurate, the next step is to compare the radiator inlet and outlet temperatures. With a cooling system in good working order, including adequate airflow through the radiator fins (VERY important), you should see at least a 30F drop at the outlet.

These two preliminary steps should help guide where to investigate next.

I'd also suggest using a cooling system pressure tester to check the integrity of the system. With the engine cold, pump up the system to the cap's rated capacity. Let it sit for about 15 minutes and make sure the pressure does not drop more than a needle's width or so.

Keep us posted.