Have a question I hope someone can help me with. On my 94 F150 5.8L, just above the thermostat housing is a "hexaganol tree" threaded into the block. It has what appears to be an electronic sensor (temp) threaded into it, and has one of the heater coolant lines running to it - and also has a smaller rubber line (5/16") that goes from it to a fitting on the bottom of the throttle body.

My question is, what is the purpose of this small line that goes to the throttle body - and is there supposed to be coolant in it? My very limited mechanical knowledge can not figure out what coolant is going to the throttle body for.

 

Hello, I'm not a mech but if it is like the 87-93 5.0 Mustangs were the coolant will run through the same way to "program" the temp of the air/fuel mixtures....

 

I thinking it must be something like that but surprised that it would need to go into the throttle body to get the heat information. It would seem like the computer would just pick it up from the temp sensor.
I'm trying to trouble shoot coolant coming out of the bottom of my heater core box....... and noticed it. Of course I'm pretty sure I know why the coolant is coming out of the bottom of my heater box. and I'm not too happy with the thought of what needs to come next!!

 

These trucks have coolant running through the throttle body. I have been told it's for emissions reasons, and I've been told it's to stabilize air temps into the T/B when the weather is very cold. Either way, it's unnecessary. There are freeze plugs in the T/B which often rot out, causing a coolant leak. There are 2 choices to fix this - replace the T/B, or bypass it. Aftermarket T/b's don't even have the coolant connections, so I chose to bypass it on mine.

Sorry to hear about the heater core - that job doesn't sound fun.

 

How did you bypass it? Just disconnect the line to the throttle body and plug both ends?

 

On mine, it has an in, and an out. I pulled both hoses off, bought a new piece, and ran it from the connection where it comes off the system, to the connection just above the thermostat where it reenters the system. Are there 2 connections on your throttlebody (an in and an out)?

 

Man, I tell you this is embarassing!! I've had this truck since it was new in 1994 and never saw this stuff..... It looks like mine enters at the bottom of the throttle body and exits up at the top and runs from a hose to a metal tube that lays across the top of the radiator and enters into the radiator in the fill neck. I even realized the two freeze plugs in the side of the throttle body just now that you mentioned. I assume you did not encounter any problems from bypassing it??

I really appreciate your help with these questions.

 

It's not one of those things we pay much attention to until we have to. I had to ask all of these questions when I had a freeze plug go. That's why forums like this are so helpful.

No difference at all in the truck since I bypassed the T/B. I called the manufacturer of the aftermarket T/B, and they don't even make one with the coolant lines, because they say that having hotter air going into the T/B detracts from performance (seems logical).