3406 B Wont Heat UP

[shopguy]

Hello ,I am working on a 85 L9000 /3406B that wont heat more than 130 ,new stat ,fan clutch still no heat. except in hard pull.Can someone tell me why the rad has two smaller hoses on the right tank one at top 3/4in.from head and one at bottom 1in. to water pump i think that is a bypass but that is the only part that gets warm, top rad hose andthe rest of the rad stay cold.should there be some restriction or check valves in the bypass ? Do thoes fittings, connect inside the radiator or does it just dump in, ?
Thanks

 

[CRAFT]

Did you think to check if the thermostat is stuck open?? .......because that is probably the 400hp version slant six, I'm not sure where Ford put it ....it's probably a defective one

 

[shopguy]

Yea it was closed up , put in a new one anyway, The hose & pipe from the thermostat to the radiator is cold ???? Thanks for your reply

 

[CRAFT]

So, I'm guessing it's fixed now .....cause you say the top hose is cold and the engine is now retaining heat until up to temp where it'll open up ?? ...YES ??

 

[Willis Bushogin]

L9000

Hello ,I am working on a 85 L9000 /3406B that wont heat more than 130 ,new stat ,fan clutch still no heat. except in hard pull.Can someone tell me why the rad has two smaller hoses on the right tank one at top 3/4in.from head and one at bottom 1in. to water pump i think that is a bypass but that is the only part that gets warm, top rad hose andthe rest of the rad stay cold.should there be some restriction or check valves in the bypass ? Do thoes fittings, connect inside the radiator or does it just dump in, ?
Thanks

I had a similar problem a few years ago and I think this was the solution
The engine wouldnt get hot, because the clutch fan ran all the time, it was the thermo switch was bad. I think I cut the air going to the clutch fan and it allowed the engine to get hot enough for the thermostat to open. I then backtracked and found the fan switch bad, or hooked up wrong. Have you got a manual switch in the cab, that you can turn the clutch fan on ? I understand the thermo switch is manual and automatic, the engine starts up, clutch fan off, engine heats up to temp that thermo switch is set at, clutch fan cuts on
I hope this helps

 

[Randy88]

By chance do you have a low flow radiator system in that truck vs a high flow system? If so how many passes is the radiator set up for? Also how long have you had the truck and is this the first time you've had problems? The reason I"m asking is because if it won't heat up to even the temp the thermostat's set for that means the thermostat's not even opening at all, does the fan run constantly even at start up? Have you put a thermometer on the block or head when the guage reads 130 to check to make sure the guage is accurate? If you could get back to me on these questions I maybe able to help you out somewhat with a low flow system, I"ve got one on one of my trucks, a totally different animal than the high flow systems on most trucks then and today.

 

[shopguy]

It is much better now ,the fan was running all time. I knew it was but i didnt know that would cause that problem with the stat closed up tight, guess with the bypass hoses to and from the radiator fan clutch is very important. Yea the guage agreed with thermometer .Tell me how much head pressure the A/C should build before it turns the fan on? I put a jumper in the switch to stop the fan now. it has an adjustment screw in it but i think i will change it, does any have one or the part #? I have heard of the low flow but never worked on one.
Thanks to everyone!