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Thermostat and Delta

3K views 11 replies 4 participants last post by  djmaguire 
#1 ·
Current delta of 13-15. EOT never gets over 185 or so. ECT runs...well...13 to 15 over that. As I understand it, ECT should be over at least a little over 190 when up to temp. My question is: How would /could an improper or bad thermostat effect the delta? What difference could I expect to see with a new "correct" thermostat? If the thermo is keeping ECT low and I'm still seeing 13-15 delta, how would a hotter "correct" thermo not make the delta worse?
 
#2 ·
First off, it looks like you have "ECT" and "EOT" swapped in the first sentence. Please verify. ECT will be higher than EOT as the engine is heating but - once steady state ECT is reached - EOT will be higher. It's the physics.

The reason why the ECT temp matters is because flow rate matters. In order for the oil cooler to work at maximum cooling capability, the coolant flow through it must be at the cooler or heat exchanger's rated/designed flow rate.

Thermostats work by restricting flow. If your coolant flow rate through the cooler is lower because of a partially closed stat, the amount of heat transferred from the oil can be lower and - as a result - the exit temp of the oil can be higher (i.e. higher delta).

Now... if something other than restricted flow is causing the lower ECT to occur at full flow, this point doesn't apply. So, it isn't some law that lower ECT means higher delta. Just that lower ECT *could* mean higher delta.

All of THAT said... I wouldn't expect much change for you. You just aren't that far off. I'd still change the stat on principle. They're cheap and it's easy. ...but I wouldn't get my hopes too high for some 3F delta to come of it.
 
#3 ·
It'd be good here to add that - although replacing a stat that's off 7F won't likely knock 7F off of your delta - replacing a temp sensor that's off 7F could.

Be sure to compare ECT and EOT readings after the engine is fully cooled. Any bias that exists there could remain or grow with increasing temps.

That or use a thermometer to measure your actual ECT and EOT at operating temp. A delta is only as valid as the two temps used to calculate it.
 
#4 ·
Thank you for your reply. You are absolutely correct. I have my initial EOT and ECT references crossed up. Sorry for the confusion.
What should the correct thermostat temp rating be? Also, I'm not sure I understand how to determine sensor accuracy. When cold, they do both start at ambient temp and increase from there..mostly in unison until the ECT stabilizes and EOT continues. I do have an IR thermometer I could use to verify I suppose. Once again.. Thank you!
 
#6 ·
My ECT stays pretty constant 190F with the OEM thermostat. An occasional jump to 192F, but that's because the PCM measures ECT in 2-something degree resolution. You're not too cold and not too hot where you are. I'd stick with OEM.

You have it right about both starting at ambient after a long cold soak. The ECT will jump off of ambient faster than EOT and lead until stat temp. Then the EOT will stabilize at its higher temp. Yes to IR.
 
#8 ·
My Torque display shows decimal places, also. It just dumps in 2.3F (or something) increments. If your ECT is moving 0.1F at a time in Torque, I'd suggest that you check and make sure that the correct PID is selected.
 
#9 ·
What he said. The ECT is reported in 1° Celsius increments, which equates to 1.8° Fahrenheit. You won't get decimal increments for ECT if the PID is correct.
 
#11 ·
Well, I have no documentation of my theory, but it seemed plausible by the way the ECT increments, so that's what I went with. Perception is reality, right?
I do remember a discussion about this very topic quite a while back. I might try to look that thread up.
 
#12 ·
Well, I have no documentation of my theory, but it seemed plausible...
More than plausible. It is statistically likely to a rather tremendous degree.

The ECT increment is 1.8° Fahrenheit and a 1.8° Fahrenheit change equates to a 1° Celsius change rather precisely, ergo the PCM operates in Celsius.

I'm fine with that.
 
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