Heater may be contributing to low temperature

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Ok, I came back from a long drive. With the Ex.
I don't usually use the A/C but I put it on. I have the fancy EATC.
Anyway, the temperature is a rock solid 194 when it was on(scan tool temp). On the gauge it is about 47% (not perfectly centered). 198 is dead center.

When the A/C is on, a vacuum valve blocks the core. Makes sense A/C would bring up temperature.

Once the A/C is off, the needle started to move again.

So, I guess the heater core is doing something. Then I found some weird TSB for this engine (4.0 OHV) about a bypass hose from the thermostat area to the lower rad hose. Long out of production. It is supposed to stop noise in the heater core or temp variations. They mentioned steam formation in the TSB. This engine does not have an external bypass, it is a narrow channel in the manifold I believe.

I still am probably going to install the other super-stat to see how it reacts. It is also a 5 deg higher stat so that should help even if it cycles. Looks like a very heavy duty unit. It was like $4 after discount. Gives me a reason to play with the truck too.
 
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Actually I'd be happy with them numbers 194 is right around where it should be...198 being exact, but take into play scan tool may not be exact and other factors... last time I checked mine with the scan tool it read 191 it was a 75 degree day out and I came back from a 45 min trip no ac on...You can play with the thermostats there not that hard to change on this motor... If you get a good constant reading let us know which stat did the trick...
 
Originally Posted By: rollinpete
Actually I'd be happy with them numbers 194 is right around where it should be...198 being exact, but take into play scan tool may not be exact and other factors... last time I checked mine with the scan tool it read 191 it was a 75 degree day out and I came back from a 45 min trip no ac on...You can play with the thermostats there not that hard to change on this motor... If you get a good constant reading let us know which stat did the trick...


Yeah, I'm probably going to be doing it shortly. The service manual has an interesting note: Coolant level may drop(1 or 2 qts, something like that) for 7500 miles after service. In other words getting all the air out is an act of impossibility. Probably a case for that vac filler.
 
If you pop off the radiator cap when the engine is dead cold it should be 100% full.

After doing a refill on both my cars it can take three or four cycles with me topping off the radiator to get all the air out and keep it full. Any leaks no matter how minor will prevent the air from being expelled.
 
Ok, I installed the Stant. It has no real "relief valve" like the OEM. Didn't drill anything. It does have V notches. The Super Stant is thicker than the OEM and looks as good or better.
Cooling system is like a new car, old thermostat looked shiny brand new, and intake manifold and elbow was clean and shiny. Coolant was changed every 30K with Green stuff.

Before installing I had both in a pot, the Ford one opened about 8 degrees before and it is quite slow to react. Stant opens at around 195 and when the flame went off it closed immediately. I would say the Motorcraft is defective but since I owned the truck there were 3 in there. The original, one changed with a aftermarket warranty WP service, and one changed at the last coolant flush. They all were similar. Maybe it is designed that way on purpose, who knows. Temp always moved around, 3 dealers said its normal and will last 400K miles. One dealer said that is one of Fords most trouble free engines. He said they have customers in the system with very high mileage and they were servicing them since day one.

Air purged easily with the Stant after the first heatup. No quick overheats due to air. Didn't even open the spill free funnel I bought, probably going to return it. In the morning I added about a 1/2 cup of 50/50 coolant to the rad.

After driving 200 miles the temperature is in the mid-high 190s in 90 degree weather up some 10% inclines. Needle sits centered, on the icon, A/C on or off. Truck warms up very quickly, about 2 minutes earlier than the last stat. I have graphs from the old stat.

So, there is nothing wrong with the truck, and I'm wondering if that OEM stat is the culprit for those TSBs saying you need bypass hoses. The hole on the OEM stat isn't tiny, maybe that contributes to it.
 
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