OK, it’s time to talk about the so-called "hot water bypass" mod that some people advocate for the 3.0L vulcan engine. These people claim that the HWB will cause your motor to run cooler by cutting off the "hot" coolant flowing through the intake.

First a little history. Starting in the '98 model year Ford started passing coolant from the cooling system through the upper intake manifold in 3.0L Ranger and Mazda B-Series engines. There are a couple of theories as to why this was done. A lot of people say the main reason was to get the engine to WARM UP to operating temperature faster, hence kicking in the engine control management system that much sooner, resulting in better emissions control and improving overall gas mileage. This seems to make pretty good sense to me. But I’ve also heard another explanation that I find quite interesting, which is as follows:

Your vulcan’s EGR system is designed to allow extremely hot (500+ deg.) exhaust gases back into the combustion chamber through the intake manifold, which gases then get mixed in with the air/fuel mixture and burned. This combining of the air/fuel mix with the exhaust gases actually causes the final mixture to burn at a lower temperature, thereby keeping the heat down in the combustion chamber and reducing NOx emissions. (But boy, does that intake manifold sure get really hot with those exhaust gases passing through it!)

Hence, another very plausible reason behind passing coolant through the upper intake manifold could be to help COOL DOWN the intake which is consistently having these extremely hot exhaust gases passing through it by virtue of the EGR system. Think of it ...hot coolant runs about what, 195 deg. or so? That is a heck of a lot cooler than the temperature of the exhaust gases that are constantly being introduced back into the intake manifold!

So according to this theory (and somewhat contrary to conventional wisdom), it could very well be that passing coolant from the cooling system through the upper intake manifold on the 3.0L is actually Ford’s way of helping COOL DOWN not only the intake manifold itself, but also the temperatures of the exhaust gases that are being fed back into the combustion chamber. That in turn helps keep the combustion chamber temperature down, and we all know how important a cooler combustion chamber is in the fight against pinging!

So, just maybe the infamous "hot water bypass" mod is not such a good idea after all.

Any comments?

 

The reason for the coolant going through the intake is to stop TB icing. When they switched to the plastic intake they move the coolant line to a coil going around the PCV hose at the valve cover. Based on this the moisture that is causing the icing must be from the crankcase. The was a TSB on the icing problem.

 

Hi Ken,

You got me on this one ...I never heard of a TB icing problem before! I guess it must have been a big enough concern for Ford to redesign the intake a little bit, is that how it happened?

And to be honest, I'm not sure how passing coolant through the intake addresses that problem?

Thanks for any feedback.

 

Well, anything is possible, I don't really think it makes too much diff one way or the other. Motors have run coolant lines to the intake manifold since water cooling was invented, and it's always worked.

I don't think it's necessary, though, so I pulled them off my 98. In two years I've noticed no loss in mileage or performance. I do however attribute the reason I haven't heard my engine ping in two years directly to the bypass and 180 thermostat I installed at the same time, which also didn't hurt my economy or performance.

The upside is if you try it and don't like it you can undo it in about 3 minutes!

 

FYI Joe.

99-23, 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.