Unexpected drop in engine temperature

[Newcsn]

For the 3 years we've owned our 2006 Dynasty w/ a 400HP ISL the engine usually runs b/t 198 & 200 and the transmission hovers b/t 200 & 203 (per the Aladdin). On each of our last two trips I've encountered our engine & trans temps unexpectedly dropping to 177-183 - staying there for a while (15-20 minutes) and then all of a sudden rising back up to their usually temps. 

My first thought was that our cooling fan was stuck wide open. So when it happened today we pulled off the road & I checked to see if the fan was running full tilt. It was not - it was just idling. I thought perhaps it was engine RPM related so I increased the engine RPM & there was no change in the fan RPM. The temps stayed right around 183.

Has anyone encountered this scenarios previously? Any thoughts as to why this might be happening? I don't mind the engine & trans running cooler - but this is very strange!

[Dr4Film]

Don't have any ideas for the drop in engine and transmission temps, however my 06 Dynasty ISL-400-02 engine Temps are about the same as yours but my transmission temps are generally 5-7 degrees higher than the engine temps.

Since both drop at the same time I would suspect a possible glitch in the gauge electronics.

Edited July 16 by Dr4Film

[BradHend]

Thermostat might be on the Fritz and staying open.  For what they cost, I’d just replace it on spec.  

Edited July 16 by BradHend

[Martinvz]

Is there any change in the coolant level in the overflow tank? I hope not but if there is, there may  potentially be a problem. 

[Newcsn]

We are grateful for this site & all the knowledge so willing shared in this group - and - thanks again for the feedback! 

13 hours ago, Martinvz said:

Is there any change in the coolant level in the overflow tank? I hope not but if there is, there may  potentially be a problem. 

There's been no change in the coolant level. Last fall I replaced all the hoses, thermostat , coolant & the overflow tank (C-Low Fab). Since then, the coolant level has remained steady.

 

13 hours ago, BradHend said:

Thermostat might be on the Fritz and staying open.  For what they cost, I’d just replace it on spec.  

I actually wondered if I got a defective thermostat last fall & if it's hanging open intermittently. I may snag a new one & swap it out.

Question: Do the dash gauges & the Aladdin system read off the same sensors? I thought I read somewhere that there are designated sensors for dash gauges & Aladdin.

The reason I ask? It seems the temps on the dash gauges dropped similar to the changes I was seeing on the Aladdin. If they have designated sensors then you'd think they would not have coinciding responses.

Thank you again!

[dl_racing427]

On 7/17/2024 at 9:07 AM, Newcsn said:

We are grateful for this site & all the knowledge so willing shared in this group - and - thanks again for the feedback! 

There's been no change in the coolant level. Last fall I replaced all the hoses, thermostat , coolant & the overflow tank (C-Low Fab). Since then, the coolant level has remained steady.

 

I actually wondered if I got a defective thermostat last fall & if it's hanging open intermittently. I may snag a new one & swap it out.

Question: Do the dash gauges & the Aladdin system read off the same sensors? I thought I read somewhere that there are designated sensors for dash gauges & Aladdin.

The reason I ask? It seems the temps on the dash gauges dropped similar to the changes I was seeing on the Aladdin. If they have designated sensors then you'd think they would not have coinciding responses.

Thank you again!

On the coaches I'm aware of, there are separate senders for the dash gauges.

[Tom Cherry]

OK....my curiosity went on OVERLOAD.

NOW....if you scroll through these and there are a LOT of good comments, I focused on our Cummins Expert...  @Frank McElroy made the following comments.

These are scattered about in the 3 pages.  Frank is concise, to a fault...LOL...

BUT, if anyone wants a primer, I think on this discussion....then read Franks' comments and/or read the entire topic...it addresses many of the comments here.

 

Both the dash gauge and the Aladdin are getting engine temp data from the engine ECM on the same data bus.  The same data would be on the diagnostic port under the dash.

data bus?

Frank do you know which ECM pin # provides output to the dash gauge? I don't see it on my schematic. My original dash gauge was analog (12V + with variable resistance sensor providing a ground path) and not digital. I never figured out where the gauge got its non- standard resistance ground  from when I replaced it. There is another sensor on the front of my engine however I cannot access it as it is completely  buried under engine accessories. So I installed a new sensor which matched the new gauge at cylinder #6  when I replaced it.

Bill I jumped the conductors at my sensor to verify that it is indeed the high temp light at the dash. It is a N.O. switch as someone suggested. 

 

This varied over the years where the gauge clusters although looking analog were actually digital stepper motors controlling the dials.  Not sure how much of you gauge cluster and warning lights get their multiplex signal over the J1939 or J1708 or older J1587 data bus.  The multiplex signal over a single pair of twisted wires handles all communications between the engine, transmission, transmission control pad, antilock brakes and dash gauge cluster computers.

Depending on the severity of the overheat, the engine will derate and possibly trigger a stop engine warning.  The overheat will also be recorded in the engine abuse history report that can't be erased.

Your ISL only has one temperature sensor.  If your dash gauge is working, the temp sensor is working.  I looked at the ISL CM850 engine wiring diagram and the temp sensor has 2 wires and neither one is grounded at the sensor.  If like you say, the sensor pins show resistance to ground, it's likely a bad sensor or a case where a previous owner added that sensor to fix a fan control issue that didn't work and they never removed it.

Take a look at quick serve that is specific to your engine serial number and you will see the location of your coolant sensor and likely no sensor in the location your seeing the disconnected sensor.

However, as others have said, this could have been a Monaco add on.  If one spade is grounded, that's why only the other spade is used.  Does your owners manual have a dash high temp light?  With your engine year, this could be a control for the fan that might have been converted to a wax controller.  On newer engines like mine the fan control is direct from the ECM.  The ECM records abuse history from the same temp gauge sensor you see on the dash.

This is what a Cummins OEM temperature sensor looks like and it is mounted below the thermostat housing.

Early ISL engines were not as sophisticated in direct electronic control of the fan via the ECM like my ISL.  From Insite software I can directly control any fan speed from 0-100% in I think 5-10% increments.

My thinking is that Monaco added a temp sensor most likely for fan speed control.  If a wax controller was installed, then you wouldn't need a separate temp sensor.

 

 

 

[Georgia Mike]

On 7/16/2024 at 6:51 PM, Newcsn said:

the engine usually runs b/t 198 & 200

When I first bought my Dynasty I converted to the wax valve from Source Engineering. My fan was running wide open and temperatures ran in the 170’s now my coolant temperatures run on average about 185-188. The only time I saw temperatures in the 190-200 was when I was out west climbing steep grades in the mountains. I had a lot of conversations with Jim at Source Engineering and he told me the Aladdin data was very accurate and that my temperatures running in the mid to high 180’s was normal. When I put the wax valve in I changed the thermostat even though the old one was probably fine. Does everyone who has an ISL 400 run around 200 all the time? 

[Dr4Film]

My ISL-400-2 runs around the 195F - 200F depending on the terrain.

[Tom Cherry]

I have consistently run around 195 - 200 dF for almost 70K. The Tranny is also consistent since it uses the same coolant. I have never exceeded say 205/6, IIRC.  Tranny will run about the same on level ground.  On moderate climbs....or decelerations....about 5/10 dF higher....of course

I was climbing into Sequoia from the WEST (Sacramento route) in late July and it was HOT.  That is a HECK of a climb.  I had to downshift and let traffic go by, but the tranny cooled down. The tranny was approaching 220 and the Engine was maybe 205.  Downshifted.  Engine cooled off as did the Tranny...but, obviously, it would be higher as it was under stress

I have the STOCK Electronic system. 

[Georgia Mike]

Interesting that you both are about 10 degrees warmer. I wonder if this is affecting my mpg because when the fan was running wide open I was averaging 6 mpg then after the wax valve install now I am 7.2 mpg. What are you all averaging? I know there are factors at play like weight and towing but I always tow a car and am loaded down pretty good. 

[Dr4Film]

@Georgia Mike On our trips to and from New Hampshire from our home in Florida we have averaged around 8 - 8.4 mpg while towing a 2006 Saturn Vue which is generally fully loaded with stuff. We usually take a different route in places when going north versus south.

[Georgia Mike]

2 hours ago, Dr4Film said:

we have averaged around 8 - 8.4 mpg

I think you said earlier that you drive at 55 so I’m sure that helps. I tend to be at 65-68 so I’m sure that doesn’t help my mpg

[Dr4Film]

Yes, that's correct. The only times I am driving faster than 55 is when passing someone which is very seldom or when coasting down any hilly rolling terrain.

With fuel prices so high I decided to reduce my speed from the 62-65 that I was using on my Windsor to 55. The Windsor ISC needed to be at 62 to keep it in 6th gear whereas my ISL in the dynasty stays in 6th gear at 55. It is a safer speed and save fuel too!

[96 EVO]

Flat land I'm at about 8.2mpg driving 61mph.

Towing a 3,000lb compact car.