Hello all, my name is Christian and I have a 1979 F350 Ranger Lariat 4x4 with the ford 400. A few weeks ago my old radiator head blew so I bought a aftermarket aluminum replacement. I also bought a JEGS dual electric fan relay kit and a electric fan shroud. The temperature mostly stays in the middle and the sensor for the relay kicks the fans off and on as needed, but as soon as I go on the highway the gauge jumps to the begging of the “A” or “L” in normal, it used to run a lot cooler on the highway. I’m just worried about summer temperatures making it overheat. It has a oem replacement thermostat so i’m not sure if i should replace that to make the flow faster or slower. i also pressure tested my hole system and it has no issues.

 

my guess would be that the fans and shroud block more air than would flow through it at highway speed. you can make some hinged flaps on the shroud that will open when the pressure inside the shroud is higher than outside. if it's not too much hassle, try removing your fans and go for a ride on the highway and see what happens.

also, you have an "OEM" replacement thermostat?? where did you get it? is it the same robertson style as sold by Tmyers??
https://www.summitracing.com/parts/s...0012?rrec=true

 

You might have got too small a radiator. I'd recommed an aftermarket temp guage to be sure where it's at.

 

Go back to the stock fan and shroud

 

okay, i’ll give that a go after i replace my temperature sensor.

 

i’m pretty sure i have the right size, it’s the same dimensions as the old one. i’m going to try to install a after market temp gauge.

 

i know my truck would overheat before i get to the highway. i’m going to get some of hinged flaps and see if that helps, but first i’m gonna install a aftermarket temp gauge. i got my thermostat at o’Reilly’s. i’m not too sure about the style of it. thanks for your help and including the link to the flaps. should i just trace out the flaps and get a dremal and go ham?

 

that's not a good sign for your system being robust enough in general.
not sure what oreilly's gave you, but this is the style thermostat you need:
https://www.tmeyerinc.com/product/thermostat-bundle/

 

Not shouting, just wanted to make my notes obvious. In a 351M or 400 or a 351C, the thermostat has a hat on the bottom that increasingly restricts the bypass as it opens to encourage coolant to go through the cooling radiator ... otherwise it will recirculate in the block and just get hotter and hotter.


CORRECT FOR 351M/400 & 351C, NOTE THAT HAT UNDER THE POWER PILL THAT WILL BE FORCED DOWN TO RESTRICT THE BYPASS WHEN OPEN, SO ALL HOT COOLANT GOES THROUGH RADIATOR.



WRONG FOR 351M400 & 351C ... IT HAS NO HAT, HOT COOLANT WILL BYPASS THE RADIATOR AND CONTINUE TO HEAT HOTTER AND HOTTER.

NOTE THAT IT TOO HAS THE HAT THAT RESTRICTS FLOW THROUGH THE BYPASS

 

Like bear said. If you got a t-stat from O'Reily's 99% chance they gave you the wrong one. In addition to the Robert Shaw (the best) and the NAPA stat, the Stant 13468 is correct also.

 

One other place I forgot about is Robertshaw 333 Series hi flow balanced sleeve thermostat – FlowKooler Hi Flow Waterpumps (flowkoolerwaterpumps.com)
And for us Cleveland folks who have the removable bypass plate they have a plate with a smaller hole that allows the use of the more common 330 series t-stat.
Robertshaw 333 Series hi flow balanced sleeve thermostat substitute & – FlowKooler Hi Flow Waterpumps (flowkoolerwaterpumps.com)

 

yup, definitely looks like i have the wrong thermostat in there. i’ll buy a new one. i feel dumb now, rookie mistake. i

 

i do live pretty far from the freeway and there’s a couple long lights, i don’t want to risk warping a head. what temperature range should i get for the new thermostat? i live in southern california and i often take the truck out to the desert. i was thinking 190*

 

Generally, for a carb motor I like cooler t-stats. personally i do 160 but 180 is ok.. i dont like over that in a warm weather or summer only vehicle

 

I’ll buy a 160 one right now.