Hello Everyone,
I want to thank you in advance for taking your time to read this post and any help is appreciated. I am not new to fixing Fords but am admittedly unfamiliar with 335 motors. I bought a 74 F-100 some time ago that has a locally rebuilt 351m and it was priced very cheap because there was more done wrong than right. I have been fixing things for years and the one thing that I am sure of is next to nothing on the truck is right or model year appropriate. The truck has always had a problem with the temperature creeping up at idle and will eventually overheat blowing coolant out of the radiator cap and overflow. The truck has a bunch of custom parts made by one of the previous owners. When I bought it, the hood would not shut completely because the custom grille hit the front corners of the hood. After I modified the grille to clear the hood, I found the radiator mounted so high up in the radiator support that the hood would hit the radiator cap also preventing it from shutting. After further investigation, I found that if the radiator was lowered to an appropriate position the unshrouded fan would hit the upper radiator hose(see pictures). Instead of digging into why the engine was mounted too high in the chassis I opted to replace the mechanical fan with a shrouded dual electric fan assembly and matching 4 row aluminum radiator. With the hood shutting properly and everything functioning, I tested it again and it still had the temperature creep issue. I started with the thermostat. It was not the correct style for 335 motor bypass and after trying to chase one down locally I finally ordered a t-meyer 160F track boss and retested. Unfortunately, the temperature creep was still there. I flushed the motor with a high concentration of prestone flush doing several hot soaks and then draining even when it seemed it couldn't get any cleaner.....no change. I found the heater core ports were bypassed with a hose running from port to port so I replaced the hose and capped off both ports and still no change. I replaced the water pump with a new, not reman, assembly and no change. I did a block test with no change in the fluid color whatsoever. Oil looks fantastic and at the proper level. I tried pulling timing and fattening up the air/fuel mixture and no change. I pulled the t-meyer thermostat and bench tested just to be sure and it works properly. When I had the water pump off, I blasted the block ports with the hose on full blast just to try and flush any remaining debris from the block but nothing crazy presented itself. I did notice that the adapter plate between the engine block and water pump doesn't seem to line up well with the coolant ports on the water pump/engine(see pictures). Every time I filled the cooling system I did so with a coolant filling kit with the appropriate adapter to purge the air from the system properly. As I said before, all the parts on this truck seem to be mismatched. The original cooling fan I removed is a D6TA-A2A with 7 blades. You can see in the pictures how high it would sit in relation to the radiator if re-installed. My current theory is I either have the wrong water pump/adapter plate or my crank/water pump pulleys are wrong causing the water pump to spin too slowly. The Crank pulley is a 4 groove D3AE-6312-CA and the water pump is driven off the pulley 2nd from the balancer which is roughly 6.5" in diameter. the water pump pulley is a single groove D1AE-8509-A1A and is just under 6" in diameter. With the diameters listed this water pump is only slightly overdriven meaning its turning pretty slow at idle. The RPM of a shaft with a pulley 5.9 inches in diameter, driven by a pulley 6.5 inches in diameter, turning at 600 RPM is 661 RPM. Summit lists a March Performance 1618-08 water pump pulley at 5.25" which would increase the speed to 742 rpm but I am not sure the crank pulley is correct either. The truck only has the water pump and the alternator to drive so if any of you know of any factory pulley options that would help, I would appreciate it. If you have any other questions on parts replaced or have suggestions on other potential issues I should chase down, please let me know.

old fan installed for reference

old fan installed for reference

Thermostat open

after flushing

Adapter plate

 

When you replaced the tstat, was the brass collar installed in the block?

 

No I did not. I have a 351M not a Cleveland so that portion is cast into the block not the press-in plate. It's my understanding that is the difference between the 351m and 400 vs the 351c.

 

My mistake, forgot the 351M/400s had it made in.

 

After looking at the pictures, what immediately comes to mind is the lack of a shroud as a major contributor why the temperature rises and not sure the fan clutch is beneficial either since you don't have AC on the truck.

 

I just popped that fan back on there to show what it looked like before I switched over with the radiator in the correct position. I have dual electric fans with a matching shroud that came with the radiator. I am considering switching to a different electric fan if the smaller water pump pulley doesn't change anything.

 

Understand. But if you don't plan to incorporate A/C, and before spending money on electric fans, consider going back to OEM configuration, less involved and proven to an effective cooling method.

 

I already have the electric fans. That was all part of the getting the hood to shut mission I talked about up top. I cannot put a shroud on the mechanical fan due to the position of the engine in relation to the radiator. If you look back at the pictures you can see the fan is around 5" too high.

 

You might have a 351C, but you do not have a 351M or a 400. The 351Ms and 400s are Clevelands in that all three belong to the 335 series, they all have 8 valve cover bolts, they can share heads, but 351Ms and 400s are taller blocks and they have a low wall where yours does not.



You need the insert to work with your 335 style T-stat. 351Cs rely on that insert just like a 351M or 400 relys on the hat under the T-stat. Just like a 351M or 400 will graddually keep getting hotter if using a wrong T-stat, the 351C will do the same without the insert under the T-stat.

 

One helluva catch tbear. I didn’t even look at the distributor in that photo. That’s a Cleveland for sure.

 

Thats very strange and god I hope you are right as that would be an easy fix. I will see if it will let me upload a picture of the bypass under the thermostat but it looks like all the pictures posted on the 351m. I will have to try and find a picture of the 351c without the plate installed. The casting number is D7TE-A2B which all the literature I have read including the paperwork from the rebuilders receipt have 351m.

 

351M or 400 looks like this below, it has a well defined receptacle for that "hat" to come down and restrict bypass, thus forcing coolant through the radiator.



Below is a insert with the same T-stat, the insert goes into the block of a 351C



Below is the 351C with insert in place.



Below is the insert if laid on the T-stat to show the close fit in the block.


Hope it helps.

Thank You ..... "Even a blind hog finds an acorn every now and then".

 

I thought something looked "off" when I saw the pictures earlier good catch tbear. It being a 351C makes sense. Based on the fuel pump block off plate, it is a 335 series engine for sure. If you measure the width of the intake manifold. 351C is about 10.5" wide and 351M/400 is about 12" wide.

351C Intake

351M/400 Intake

Since it is a '74 F100 I am guessing it came with a 300 Six or 302, both have the same bell housing as 351C. I am leaning towards 300 Six originally. If I am not mistaken the frame perches are a bit taller for the inline-6 compared to perches for the V8s. That would explain why the engine sits high and you have a hard time fitting fans. If you have the VIN handy we could decode what the truck would have come with from factory.

 

Looks like the 351m
I had already compared the photos and was sure it was a 351m. I attached the photo just so everyone can see what I have got. The vin is F10YRT26888. I don't know how, when or why this motor ended up in here but I am with you in guessing it was probably a straight 6. I didn't realize the mounts were higher on those so that is good to know. I would rather have a mechanical fan so if I can find the correct parts I might just go that route.

 

F10YRT26888

F10 = F100

Y = 360ci Engine

R = San Jose Assembly Plant

The T26888 is the sequential number assigned based when it was built. What I had handy to decode didn't cover that detail.