some rangers do have them.

no, there is a coolant jacket or a line that allows the coolant in the tb to circulate with the rest of the coolant, kinda like on the engine block.

 

They put it on there to stop TB icing, my 2000 3.0 has coolant lines coming off the heater hoses going to the upper intake right after the TB. The 2002 3.0 has it wrapped around the PCV hose. I bypassed it and didn't notice anything so I put it back they way it came from the factory.

 

All in all, I checked again, and my 04 4.0 sohc does not have any coolant lines to it, or close enough to it to cause any confussion, so whats this guy talken about?

 

I kinda doubt they're there for throttle body icing. I've NEVER heard of a throttle body on a fuel injected motor icing up. On a carbureted engine? Yeah, it is a probelm on some updraft and sidedraft designs (hence why most carb'd aircraft have carb heat) but usually it isn't an issue on vehicles that place the carb or throttle body over the block.

While it is true that there is a pressure drop across the throttle body in a FI engine, it is nowhere near as great as one in a carburetor, which relies on the pressure differential to draw fuel out of the bowls. Therefore there isn't much of a temperature difference from one side of the throttle body to the other.

 

Woah, not true!! There is a higher pressure differential across the TB on a FI engine! With a carb, the air velocity is high across the venturies, which is above the TB (down draft carb). Therefore there will be vacuum above the TB on a carb, no vacuum above the TB with FI.

 

Article No.
99-23-5 THROTTLE - STICKING OPEN OR CLOSED DUE TO THROTTLE BODY ICING - IN EXTREME COLD AMBIENT TEMPERATURES - VEHICLES BUILT THROUGH 7/1997 WITH 3.0L 2V ENGINE
LEAK - ENGINE OIL LEAK FROM TOP OF OIL LEVEL INDICATOR TUBE - VEHICLES BUILT THROUGH 7/1997 WITH 3.0L 2V ENGINE
PCV SYSTEM - MOISTURE FREEZING IN PCV SYSTEM - IN EXTREME COLD AMBIENT TEMPERATURES - VEHICLES BUILT THROUGH 7/1997 WITH 3.0L 2V ENGINE

Publication Date: NOVEMBER 2, 1999

FORD: 1995-97 AEROSTAR, RANGER


ISSUE:
During extreme cold ambient temperatures and under certain driving conditions, moisture in the crankcase may enter the PCV system, freeze and cause pressure in the engine crankcase. The PCV fitting in the upper intake manifold may freeze or the fresh air line may become blocked. It is also possible, but less likely, that ice may build up on the throttle plate or the throttle body and cause throttle sticking.

ACTION:
Install the PCV Kit released for service. Refer to the Instruction Sheet included in the kit for installation details.

 

Hold on...if we're talking about ABSOLUTE pressure, ie., pressure measured from zero, then I bet there's still less of a pressure drop across a FI throttle body than there is a carb. In order to accurately measure this, you'd have to have a flow bench, but it could be somewhat accurately measured using an absolute pressure gauge to measure the drop in absolute pressure from one side of the throttle plates to another in each situation. Then you can compare the relative difference in pressures. Otherwise you're comparing apples to oranges, since as you pointed out, a carb has a lower ABSOLUTE pressure ahead of the throttle body than a FI car does. That's exactly why automotive engineers usually talk in terms of manifold absolute pressure instead of vaccum.

As the TSB Ken provided, icing in a FI engine is only going to happen in extreme cold. On the other hand, carb ice can form even when temperatures are in the 70s if the humidity is high enough.

 

Read my post, I said "differential".

 

OK, so the intake air temp at the upstream side of the throttle plate on a carbed engine is lower than that of an SEFI engine for a given ambient temp. Regard that as pre-cooled. The issue here is icing at the throttle plate itself, not downstream of it. And as I noted earler, it's the rapid (dramatic) increase in velocity, subsequent pressure and thus temp drop that causes this. If a guy breaks out his calculator and any decent college level physics or fluid dynamics textbook, there are a couple of handy dandy relationships including Bernoulli's principle that fit the situation here quite well.

I'll prime the pump for you, you can complete the calcs to estimate the temp at the throttle plate. Take for example a 4.0L (244 CID) engine and calculate the flow rate at 2,000 RPM. Assume an intake air temp of 35 degrees F, and use the air pressure at sea level, 14.7 psi. Next assume a 2 5/8" dia inlet tube and calculate the velocity in that tube (Q=VA). Now assume the throttle is open 10% (pretty reasonable for 2,000 RPM on a vehicle cruising @ 50 MPH) and apply the continuity equation, (A1)(V1)=(A2)(V2) to find velocity right at the opening around the throttle plate. From this, apply Bernoulli's principle to determine pressure and finally apply (P1)/(T1)=(P2)/(T2) to solve for the temp at the throttle plate. Along the way you will notice that in Bernoulii's equation (used to calc the pressure at the throttle plate) the velocities are squared. This is where the effect of the high velocity at the throttle plate will show. The pressure differential issue situation between carbed VS SEFI will become a mute subject.