Can anyone here put together a linear temp line of what systems control the Duramax temperature and when they are engaged?

Also how to tell if each is engaging at the proper temperature?

Are you asking about temp control of the coolant? There are two thermostats that open at diff. times. One is a typical no go stat, the other is a bypass type stat.

By their nature most tstats will have variance from one to the other. However the majority of good working stats will be in the same range.

There has been a lot of testing and data on the stock tstats, I am not sure if it is still available, but this one guy from Texas probably has it handy.

What "systems" exactly? Are we talking fan, or what?

Also please limit this discussion to the cooling system function, if this concerns overheating it needs to be moved to the overheating thread.

Yes only the cooling system. All systems, for example thermostat 1 opens at x temp, thermo 2 opens at x, fan starts at x.....

Yes only the cooling system. All systems, for example thermostat 1 opens at x temp, thermo 2 opens at x, fan starts at x.....

Rear thermostat begins to open at 180*, front thermostat begins to open and close the bypass at 185*, bypass is closed by 195*, stats continue to open until around 220 ish they max out, usefulness is around 210 ish though and the rear stat is done opening before the front stat as it has less possible travel.

Under low RPM the engine fan generally will come in around 208* but some fans are early risers and come in at 205* and some fans sleep late and come in at 210*. Under rpm above 2700 the fan has difficulty engaging due to centrifugal force pumping out the drive fluid as it is being pumped in, so the fan can come on as late as 227* or more :eek: under high rpm. Let off the throttle for a sec, it will come in.

Once ECT reaches 196* the fan is generally looking to go back into slip mode.

If you have more questions, ask away. :)

couldn't have said it any better myself!!!!! exellent discription.

Thanks!
What is the ideal operating temperature (target temp) and normal variance?

If you have an early riser fan it looks like the thermo and fan will be fighting each other as wouldn't it be safe to say if a fan is an early riser it's also turns off at a lower temp (even below the bypass temp)?

Thanks!
What is the ideal operating temperature (target temp) and normal variance?

If you have an early riser fan it looks like the thermo and fan will be fighting each other as wouldn't it be safe to say if a fan is an early riser it's also turns off at a lower temp (even below the bypass temp)?

Most trucks settle in around 192* on average and working load temp can be anywhere from 192* to even 214* stock so they won't be fighting each other, but I do see your approach. If a fan had too low of a disengagement point it would get "stuck on" so to speak at a low speed once things reached an equilibrium.

At 196 we have the thermostats restriction the coolent flow and the fan engaged cooling this restrictive flow and adding load to the truck.

I would thing the fan should only come on if the thermostats are fully open and the temp is still rising. If the fan comes on at 205 and off at 193 (early riser) it seem there will be a loop generated where they are fighting eachother. On at 210 seems to be about right if the fan shuts off at 198 because at this temp you still have room for the thermostats to try and cool the load with out the fan and it's still shutting down a little above our target temp. Do you agree?

210* is a better temp for the stock fan yes, because it will then be acting upon the full coolant flow and will make the most impact. You can also assume that normal coolant flow with the available airflow is unable to maintain control. I would like to see it off at 200* having assumed the cooling system has things under control, its span is to wide.

You could run it at a lower temperature range but it would be an annoyance.

Great, an expert agrees with me! Maybe I'm not as bad as they say. haha
This may be why my gas milage always is in the 13s.

I always thought that was just the way my truck was supose to sound, but then again I have very bad hearing and did not notice too much. Now how do I prove it to the dealer...

If your fan is staying on in a low engagement it will be equal to always running the A/C on max, it may be equal to running as many as 3 of the modern A/C compressors constantly. Mileage will surely suffer.

You can adjust the engagement ;)

Are the thermostats considerded to be pretty accurate?

The ones I have measured have been right on. I doubt they would be off enough to alter flow enough to have an effect of fan ops.

The fan never really truly disengages by the way, nor does it ever totally lock up. There is enough slop to make a difference in the amount of fan you get. Slip mode, fan totally disengaged, will be anywhere from 20%-30% of input shaft speed. Full engagement will be 80% to 90% of input shaft speed. It is likely that an "early riser" will be more of the 30% to 90% variant as it engages easier. The 30% variety will hurt mileage at all times.

We on the same page?

Great topic!

If your fan is staying on in a low engagement it will be equal to always running the A/C on max, it may be equal to running as many as 3 of the modern A/C compressors constantly. Mileage will surely suffer.

You can adjust the engagement ;)Are you talking about adjusting the OEM fan engagement? If so, I'm curious, how do you change it?

Can the OEM fan clutch degrade with miles and become an early riser?

I saw it somewhere but don't know were. Something about a secret fan mod. You have to scrape out the silicone where the element is in the front of the fan clutch and move it sideways a fraction and reapply fresh silicone to hold it in place.

How do I test when the fan actually comes on? Will the dealer replace an 'early riser' clutch?

Are you talking about adjusting the OEM fan engagement? If so, I'm curious, how do you change it?



http://www.coolmyduramax.com/forums/...ghlight=spring (http://www.coolmyduramax.com/forums/showthread.php?t=326&highlight=spring)


How do I test when the fan actually comes on?

You will need a way to read the exact temp from the data bus. I have a preditor that will read the ECT. When the truck isn't loaded my fan doesn't lock up when I am cruising down the interstate in hot temps (95*+) but it does when I slow down from cruising speeds. Like exiting the freeway or having to slow down for traffic. It is very annoying especially when trying to accelerate to pass, I have had lock up with ECT at 199*.

Did you mod your fan clutch?

The problem seems to be that in the clutch does not disengage at a reasonable temp. In your example at 199* the rear thermo is 76% open and the front is only 60% open. Since the fan is actually adding load (btu's) it just makes matters worse. Even a late riser fan will not disengage at 199* as far as I can tell.

http://www.coolmyduramax.com/forums/...ghlight=spring

You will need a way to read the exact temp from the data bus. I have a preditor that will read the ECT. When the truck isn't loaded my fan doesn't lock up when I am cruising down the interstate in hot temps (95*+) but it does when I slow down from cruising speeds. Like exiting the freeway or having to slow down for traffic. It is very annoying especially when trying to accelerate to pass, I have had lock up with ECT at 199*.
Thanks for the link! I'm going to have to play with it.

Did you mod your fan clutch?

The problem seems to be that in the clutch does not disengage at a reasonable temp. In your example at 199* the rear thermo is 76% open and the front is only 60% open. Since the fan is actually adding load (btu's) it just makes matters worse. Even a late riser fan will not disengage at 199* as far as I can tell.

No I haven't done the fan mod yet. I wanted to do some more testing first so I would have something to compare the after mod results to.