You are not logged in or registered. Please login or register to use the full functionality of this board...

Caterpillar C-13 ACERT Coolant Temp Fluctuation

Spent the morning cleaning out the header tank. Scale buildup and rust! Not fun to remove. Used a pressure washer and finally got rid of the junk. I’ll post pics later. A updated tank is in the future. 

Replaced thermostat with a genuine Caterpillar Water Temperature Regulator and updated temperature sensor. 

Using Caterpillar engine cooling system cleaner and distilled water, I ran the engine for 1.5 hours. 
The engine achieved and stabilized at 190*. 

I had closed the dash heat manifold valves. After an hour of running the engine I opened the valves. The engine temp dropped and eventually recovered and stabilized. 

I’m confident the engine thermostat contributed to the cooling issue. 

I drained the cleaner from the system and have filled it with distilled water. Tomorrow I’ll run the engine to operating temperature, drain, and add new Cat ELC. 

On the Hydraulic Fan front... I replaced the valve that is used to adjust system pressure and returns fluid to the reservoir tank. Until I drive the coach I won’t be certain if there’s a difference how the fan and radiator perform. 

Long and productive day, I’m glad Richard talked me in to working the problem myself. 

Kristi & Jeff King
Bentonville, AR. 72712
2005 45’ Newell Coach #744 
ZF Suspension/Active Steering Tag Axle
CAT-13 ACERT 525HP Allison 4000 Trans.


Great write up....please post some pictures and any gotchas that you encountered along the way. Thanks for sharing your journey on sorting out the issues.

I drove my coach in the hills in northern Arkansas yesterday and my engine stayed between 186 and 190f and my transmission between 190-210f. Allison transmission has a “performance” button. That makes the transmission shift more aggressively which is great for the mountains. It downshifts faster making more RPMs which is good for the cooling.


Bill Johnson
Birmingham, Alabama

I uploaded the new Cat ELC this morning... yes literally uploaded it with a fantastic device called a AIRLIFT.
It made the coolant system cleaning, flush, and adding back new ELC effortless.

Getting ready for a test drive. Will provide a summary when finished.

Kristi & Jeff King
Bentonville, AR. 72712
2005 45’ Newell Coach #744 
ZF Suspension/Active Steering Tag Axle
CAT-13 ACERT 525HP Allison 4000 Trans.

Test Drive... Success!! 

Bentonville Arkansas to Neosho Missouri via I-49 and return. 
OAT 75*
Route has several grades that test the engine and cooling system. 

After the engine warmed up the coolant temp was steady at 190* plus or minus 5*. The temperature remained constant pulling the grades at 75 mph. 
It would appear that I resolved the fluctuating coolant temperature issue. 

A related issue I experienced while climbing the mountains in Colorado was high coolant temperature. Of course we suspect the radiator and hydraulic fan system. I thoroughly cleaned the radiator and have replaced components of the hydraulic manifold. I’ve got a new fan solenoid on order. 

So, has the radiator and fan been wrongly accused? Possibly so but they’re still suspect. 

The thermostat I removed from the engine is not a Caterpillar part. When I removed it from the housing I  gave it a quick look and set it aside. I was focused on putting things back together, flushing the system, and get it back on the road. The boss wanted to get away for the weekend... 

If you’ve never “serviced” your coolant system I can tell you this. You have lots of time to think about the situation. I ran the engine for an hour and a half with the Cat cleaner and distilled water. Then I flushed the system in a similar manner. During my test drive it finally occurred to me that my problem could be a thermostat that randomly sticks. Sticks open, closed, half way, and maybe even works normally...sometimes... 

I took another look at the old thermostat. I’m certainly not a forensic mechanic, if that even exists, but I’m fairly certain the galling and unusual wear patterns on the thermostat may substantiate my new suspicions.


What I do know know is I have a engine that behaves like it was designed to do, has a relatively clean radiator and engine block, and updated parts. 

My takeaways... 
Clean the radiator often. The road is a nasty place. Don’t just hose it out, spend an afternoon with it. 
Verify how old your coolant is. If you’re not sure change it but thoroughly flush the system and don’t forget about the dash heater system and preheat system. 
Caterpillar recommends changing the thermostat on a regular basis. I was told every five years would be a good idea. 
Obviously monitor your engine parameters and track trends and changes.  
Keep a log book of things you notice and do to your rig. 
Only use genuine manufacturer replacement parts. Yes I add aftermarket items but on some things, Cat in this case, it pays to go with the original. 
Plan your repair, replace or fix time limited items as long as you’re at it. In my case, I had a limited time frame. I would have liked to replace other items such as the silicone coolant hoses. You’ll probably need to order parts and some may take a while to come in. 

Working on your rig yourself is rewarding and can be frustrating. If you are confident and competent you’ll end up with a job well done and no doubt you got what you wanted. Another few perks, you get to know your rig intimately and can upgrade parts or systems. You may also stumble across another issue or problem you can also correct or get out ahead of. On this project I found a oil leak that I hope will be corrected by simply tightening a few bolts. We’ll see...

What else.... 
As I mentioned, my “header tank” had scale buildup and rust in it. I’ll replace it with a new stainless steal or aluminum tank. I also found out that the coolant sensor needs to be relocated below the level of the sight gauge, a change that came on later Cat 15 models. Might even add a recovery tank. 
Replace the radiator someday when my pockets are full of money. Yes it will likely need to be done. 

A big thank you to everyone that has helped me with this journey. I certainly hope my findings may help someone else recognize or solve a issue they have. I’m happy to answer any questions and will post a few more pictures of the work I did. 

Take care!

Kristi & Jeff King
Bentonville, AR. 72712
2005 45’ Newell Coach #744 
ZF Suspension/Active Steering Tag Axle
CAT-13 ACERT 525HP Allison 4000 Trans.

Wow - awesome write up and information. My coach does not come anywhere close to this level of sophistication. However it is amazing to see and hear the troubleshooting skills of people on this site.

John and Marcia Marshall 
1975 Newell 30ft - 9.0 IHC
1986 Navstar 9.0 Diesel 160hp
98 Mustang GT
getting closer
ASE Master & Computer Admin
Love old tech  Idea

Here is a list of the parts I purchased to resolve the engine coolant fluctuation and high temp. I’m including photos to give you an idea of what’s involved to complete the work. 

As a reminder, Caterpillar C13 Acert engine for 2005 model. Limited number of Cat 13s used in production. 

Genuine Caterpillar Replacement Parts
Temperature Regulator 247-3133
PTFE Lip Seal 3S-9643 (temperature regulator seal, used Cat tool to seat the seal).
Valve Assembly-Vent Line 239-8135
Press-In-Seal 227-5075 (seal between upper and lower regulator housings)
CN Sensor Temp 264-4297 (updated temperature sensor)

6V-6609 used on Temp Sensor 
7L-6580  used on metal tube that extends down from upper coolant regulator housing. 

Coolant and Coolant Cleaner
Cat Coolant System Cleaner 4C-4611 (2 gal)
Coolant Cat ELC Premix 238-8648 (17 gal)

Tool Purchased
Caterpillar Seal Inserter 221-8647 used to inter the temp regulator seal into the housing. 
AirLift- used to fill coolant system utilizing vacuum.


Kristi & Jeff King
Bentonville, AR. 72712
2005 45’ Newell Coach #744 
ZF Suspension/Active Steering Tag Axle
CAT-13 ACERT 525HP Allison 4000 Trans.

jeff, thanks for you very clear and complete writeups. this is exactly what helps many others.


2002 45'8" Newell Coach 608  Series 60 DDEC4/Allison World 6 Speed HD4000MH



Kristi & Jeff King
Bentonville, AR. 72712
2005 45’ Newell Coach #744 
ZF Suspension/Active Steering Tag Axle
CAT-13 ACERT 525HP Allison 4000 Trans.

Two year delta... (update):

Today is Wednesday September 21, 2022. We have been parked at the Tiger Run Resort since Sunday afternoon. This is the first time we've been back in Colorado since 2020 when I originally discovered I had a cooling issue which has now grown to include the hydraulic system. A significant amount of time has been spent on this journey by several people and I believe we are slowly zeroing in on the problem or should I say problems. 

When we conclude this journey I will provide more detail about paths taken. I can tell you this, I know more about this coach than I ever expected to in less than four years of ownership. If you've seen my post about the ZF Suspension I will tell you that is one of the paths we've been down.

Here's some info I gathered recently that might be interesting to some of you.

Specific to the 2004 Cat-13 Acert. 

The engine ECM controls a 12v DC relay that controls the hydraulic fan solenoid in the hydraulic manifold block. When the coolant temperature rises above 217* F the ECM removes the 12v supply to the relay. The solenoid piston moves to FAN High or max speed position for the engine RPM and hydraulic pump flow and pressure. The ECM will apply the 12v to the relay when parameters return to normal. The engine ECM will also call for FAN High if other parameters are out of limits such as intake temperatures or loss of inputs from sensors. 

In the normal fan operating mode, the fan speed is approximately half of the engine RPM. A few examples I recently recorded using a photo tachometer are:
Engine idle 600 rpm/Fan rpm 251
Engine 1000 rpm/Fan rpm 491
Engine rpm 1500/Fan rpm 758

When fan is in the High mode
Engine idle 600 rpm/Fan rpm 580
Engine 1000 rpm/Fan rpm 1012
Engine 1500 rpm/Fan rpm 1428

This is how the system was designed to run as explained by a engineer at Tulsa Oklahoma HydraQuip. 

A quick phone call to the CAT RV Hotline 877-777-3126 provided the following coolant temperature information:
Max coolant temp is 225*. Damage may start when engine coolant temperatures exceed 225*. C13 heads can warp.
Normal upper operating range is 220*.
Ideal operating temperatures are 195* to 212*.
The coolant regulator (thermostat) starts to open at 190* and will be full open at 212*.

I can tell you that after I replaced the regulator, flushed the coolant system, replaced with CAT ELC coolant, thoroughly cleaned the radiator... the engine ran consistently at 195* most of the time. WHY??? because the fan was always on HIGH! Please check out your system to ensure proper operation. I've been told some owners want the fan on high always but that is their choice not a system that is not set up properly. 

Here's a few picks of the manifold "block" and the solenoid "piston"




Kristi & Jeff King
Bentonville, AR. 72712
2005 45’ Newell Coach #744 
ZF Suspension/Active Steering Tag Axle
CAT-13 ACERT 525HP Allison 4000 Trans.

Tuesday September 27, 2022

Recently while vacationing in Breckenridge Colorado at Tiger Run RV Resort…

I decided to add a circuit to manually send the cooling fan to max speed

My wife Kristi was thrilled by my mechchanicalvacation skills. 

As mentioned before, in the normal mode, the Engine ECM applies/sends 12v DC to a relay (in the right engine bay electrical cabinet) that is wired to the cooling fan solenoid mounted in the hydraulic manifold block. 

At coolant temperature of 217° the Engine ECM removes the 12 v DC to the relay which in turn removes 12v DC to the solenoid and sends the cooling fan to max speed. When the coolant temperature is reduced to nothing temperatures the ECM will apply 12v DC again a fan speed returns to normal.



I identified three spare wires in the right side engine bay electrical cabinet that ran up to the forward electrical area in front of the passenger seat. I eventually used two of the three wires to control a new relay and a indicator light when I manually put cooling fan in max speed


My initial idea was to add a new five pin relay to manually interrupt the ECM 12v DC signal to the fan relay and turn on a indicator light at the driver’s position. I wired everything to fail such that original configuration will not be impacted. 

I mounted the relay in the right side engine bay electrical cabinet and ran the ECM wire through the new relay and on to the original fan relay. 
I used one of the spare wires (blue/red) to provide the ground to the new relay from a spare switch in the left driver’s control panel. The switch provides the ground to the new relay. 


I used the second spare wire (blue/black) to turn on a LED light at the driver’s position when the relay interrupts the ECM 12v DC signal. The LED power is provided by the new relay. 

This is temporary, I’ve order a 8mm indicator. 

So why did I do all this work?
I want to have full control of the hydraulic motor that drives the cooling fan. If I see the coolant temp trending towards a temperature above 212° I can send fan to max early so the coolant temperature reverses the upward trend. 

Keep on mind, on my coach, the coolant fan’s RPM is dependent on the position of a plunger associated with the solenoid in the hydraulic manifold block. In “normal” mode (electromagnet energized) the cooling fan is rotating approximately half of the engine RPM. 600/300, 1000/500, 1500/750 etc. I checked these ratios with a photo tachometer, variation does exist. 
When the fan is “sent” to max by removing the solenoid’s 12v DC signal, the cooling fan rotates at a RPM that is close to the engine RPM, 600/600, 1000/1000, 1500/1500 and in theory, so on and so on…

When we left Breckenridge and headed east on I-70 I did my best to set myself up for success.
Engine driven A/C OFF.
Dash defroster set to hot with fan on high (rooftop ac on cold).
Limited transmission usage to 5th gear primarily using gear 3 & 4 on steep grades up and down. 
Used transmission PERF mode.
When able I tried to keep throttle position around 80%. 

I carefully monitored the coolant temp and when it exceeded 212° (coolant regulator/thermostat wide open) I placed the cooling fan in max and strived to maintain 1600-1800 engine RPM. 

Jumping through all these hoops kept the coolant temperature in a very comfortable range and it never approached temperatures that would possibly breach the CAT recommended maximum temp of 225°. 
A couple of times, I allowed the engine ECM to send fan to max to verify the system was functioning normally.

My future plan is to verify the hydraulic fan motor is functioning properly and investigate possibilities with improving radiator stack efficiency. 
I’ll also be installing an annunciator light for when engine ECM removes the 12v DC signal and another annunciator light when I manually send fan to max. 

Yes… I like switches and lights… and control! 

Take care,

Kristi & Jeff King
Bentonville, AR. 72712
2005 45’ Newell Coach #744 
ZF Suspension/Active Steering Tag Axle
CAT-13 ACERT 525HP Allison 4000 Trans.

Forum Jump:

Users browsing this thread: 1 Guest(s)