coolant temperature not making sense

[jmcclesk]

When I use a cheap scanner I get coolant temps of 213f to 218f driving freeway speeds. stop and go traffic the temperature goes up to 230f. at approximately 228f there is a noticeable increase in fan speed. thinking that the car is over heating I pulled out my temperature gun and started taking readings. the highest temperature I could see with the gun was 190 to 195 at the upper coolant hose connection close to the engine side. looking at the scanner at the same time I saw 233f. i then used a immersion probe in the degas bottle and saw temperatures in the low 180f.
i also noticed that the Lincoln has no coolant sensor just a cyc head temperature sensor.
could the scanner be using the cyc head temperature as ect sensor. thanks in advance.

 

[jmcclesk]

oops 2005 Lincoln ls 3.9l

 

[joegr]

It sounds like you really have a (marginal) problem to me. Those IR temperature guns read surface temperature. I would expect the surface of a hose to be cooler than the coolant inside it. The hose material is an insulator. The CHT is located where it should be the hottest part of the engine, so I can believe that it would be warmer than your other readings. The degas bottle has little circulation, so it is generally much cooler than the actual coolant loop.

Your LS does have a combination coolant and oil temperature sensor mounted on the oil filter adapter, near the oil-to-water cooler. At that location, oil and water temperature should be about the same. In any event, it is the head temperature that counts the most.

When was the last time that ALL of the plastic cooling system parts were replaced?

 

[jmcclesk]

new parts in the last 2 weeks
water pump
radiator
all plastic parts replaced with t-stat
all hoses new except the hoses that go into the heater core.
de gass bottle

 

[jmcclesk]

return temperature from lower radiator hose in the 125 to 130f range.

 

[joegr]

Did you by chance go aftermarket on any of these, especially the thermostat and housing?

 

[jmcclesk]

yes napa and rockauto parts. For the rockauto parts I did go with the best plastic parts they had. I have tryed 2 t-stat with housings one from rockauto one from Napa auto parts. FYI no parts are dorman.

 

[jmcclesk]

do you think the scanner is using the cyc head temperature in place of the ECT?
some of the hoses from rockauto are ford hoses

 

[joegr]

Doesn't matter. You have a real problem, and it's the same one that others on here have had. You need the Motorcraft parts. The aftermarket ones do not allow enough coolant flow.

 

[jmcclesk]

the aftermarket t stat and housing doesn't allow enough flow? is that what you are saying?

the reason I'm hung up on the ECT temp is if the scanner is using cyc head temperature in place of a real ECT reading. then the 230 make sense. I see it all the time on the v 10 cng Van's at work. they there is always a large difference between ECT And Cyc head temperature [20 to 30f] higher.
thank you the information joe

 

[joegr]

the aftermarket t stat and housing doesn't allow enough flow? is that what you are saying?...

YES

 

[jmcclesk]

thank you joe, at this point what's an extra 60.00 for a t-stat and housing.

 

[FDR]

It doesn't matter if it's a $15 scanner or a $1500 Snap-On. It's reading the same OBDII data and displaying the number the PCM is reporting

 

[jmcclesk]

I understand that my question is which sensor the pcm is using. the sensor on the oil cooler or the cylinder head temp sensor. I guess I will unplug the sensors while running and see if the ect temp changes or if the pcm is using an Inferred value.

 

[joegr]

Engine temperature is from the CHT. The coolant/oil temperature sensor reads the temperature of the coolant returning from the radiator. This can be useful for determine what fan speed to use, but not for actual engine temperature.

Jaguar (on the 4.2) includes a temperature sensor for coolant temperature at the thermostat. The LS does not have this.

 

[Stevep-05LS]

Just chiming in on this, I recently swapped out my T-stat and housing to Motorcraft after trying 3 different brands because my radiator cooling fan was running steady although the system was not overheating, it was at the top of the heat range. Once I put the Motorcraft T-stat and housing in the fan hasn't run yet and the temps are 20-40 Deg lower. The opening in the T-stat is probably 1/2" diameter larger on the Motorcraft than all the others. I to swapped many parts before getting this, water pump, recirc pump, radiator, all the plastic parts around the T-stat and the radiator reservoir tank. I had measured the voltage from temp sensor and found it to be correct. The gauge seemed to be in the normal zone but the OBD reader read on the high side before swapping the T-stat. If it were me know what I know now I would swap the T-stat to the Motorcraft and I'm pretty sure you'll be good. Joegr would probably concur.

 

[Stevep-05LS]

I tried to search some pic's that someone posted on this forum showing the difference in size but couldn't find them again. JOEGR do you recall seeing some pic's, I'm amazed that the other guys would even consider making them a different size, it's so frustrating.