In the process of trying to determine the cause of my mysterious power loss I noticed today while driving that the engine temp. was cycling at what seemed to be a pretty regular interval. It would cycle between just about 190 and around 165/170. This was while driving at a steady speed of 60mph with outside temp. at 64 degrees. It even continued to cycle while going downhill with my foot completely off the throttle. I tried to time the interval and it appears to be about every 30/40 seconds. It doesn't hold at either end of the cycle. As soon as it hits around 190 it begins to drop and as soon as it hits around 165/170 it goes back up. The fan does not appear to be running. Any ideas? Is this normal?

 

It does not sound normal to me at all. When was the last time you changed your thermostat? That's where I would start....

 

Dogman, have you changed your thermostat lately. I just changed my coolant and thermostat and now I have the same problem as you.I haven't noticed any drop in power or mileage from it.Before with my old thermo it was rocksteady on 190.My new thermo did look a little different.I wish I wouldn't have thrown it away.It sounds like our thermos are either full open or full closed.

 

My truck does the same thing, depending on whether it can get up to X temperature and remain there due to load or outside temperature.
The deal with this is that the cooling system on these trucks is so large. The engine heats up, opens the thermostat and flows the cool water from the radiator into the engine. That water is so cold that it doesn't heat up sufficiently to maintain the open thermostat when it reachs it and the thermostat slams shut. Meanwhile, the hot water that just hit the radiator is cooling, and will cool off significantly by the time the water in the block heats up enough to open the thermostat again, then the process starts over again because the water in the radiator has cooled off so much.
You won't see this behavior much at 90 degrees, but at 64, as you mentioned, it's probably going to be a regular thing unless you are towing/hauling something.
Some trucks may not seem to do this because of the old thermostat, which may not be closing all the way when cold, or opens too soon when heated, and allows more flow of the cooling system so temps become more uniform between the engine and radiator.

Chris

 

I just had the cooling system seviced in June prior to leaving on a trip to New England states and Nova Scotia. This is the first time it was done since I've had the truck. The first time I had the power loss problem (see post on Sept. 8 on this forum "transmission problem or engine problem&quot was about two weeks after having all the service done prior to the trip. I had the cooling system done as well as the transmission, engine oil and filter and fuel filter. I assume they put in a new thermostat but not really sure of that. All service was done by the dealer. I don't think the engine temp. cycling is causing the power loss but its just something I noticed that does not appear to be "normal".

 

I've noticed that as long as my temps are below 160 or so, I don't have that much power. When it gets up to temp, power is great and the temp guage hangs in there at 185-190. Very little waver.

 

might want to check for air in the cooling system. look to see of there is anything in the overflow tank. then with cold engine remove radiator cap and pake sure system is full. sometimes when antifreeze is changed not all the air gets purged from the system. at times when this happens the sensors pickup the incorredt temp and adjust the engine performance till it is at the proper tempature.

 

DSLDAN,
That's an excellent possibility. I hadn't thought of that, mainly becuase my cooling system hasn't been into lately.

Chris

 

This is staight from Cummins
Summary: ram isb temp cycl characteristic

Solution:
Thank you for your email. What you are seeing is normal, though we admit it seems a bit unusual compared to passenger car (and previous) experience. The change is omitting the "bleed hole" in the tstat and having a tight seal, both of which serve to allow the coolant to come up to temp; with the previous tstat there is always some flow, and the robust cooling system heat-rejection capacity would delay the engine coming up to temp - hence the reason for the change.

Here's what we usually say on the subject: This is to address cycling of the coolant temperature in your Dodge Ram 24-valve Cummins ISB. We have discussed this and have seen it before, and what you are likely experiencing is a normal phenomenon. A brief explanation, but first we will include the caveat that exact temperatures are subject to the sensor and gauge that Chrysler provides; they may be accurate or they may not be - but what you are seeing is relatively normal, especially if you are talking about running at light loads.

A little history; In the earlier 12-valve engines, the thermostats had solid metal contact and some "pins" - the result was that sometimes they would not close completely and coolant would sometimes bypass so that under light loads the engine would not come up to full temperature. With the 24-valve, the thermostat design was changed so that the valve part does not seat against metal but against rubber, so that a tight seal is obtained; the thermostat remains closed and the engine reaches temperature.

With a heavy-duty (high capacity) cooling system in place - which is needed for higher load applications - when the engine reaches temperature, the thermostat (tstat) opens, the coolant enters a large capacity (from volume and heat transfer perspective) radiator, and the coolant immediately drops way off in temperature, the tstat closes and the cycle starts all over. If any appreciable load is applied the tstat will stay open enough to not cycle in this manner.

If you are driving easy and it's cold out you may see this cycling phenomenon; it is not a problem - alternatively, if it's warm and you're running at moderate speeds you may have a sticking tstat and you should have the dealer take a look at it.

As far as sensor/gauge accuracy is concerned, the only way to check that is with a thermometer or calibrated sensor/gauge - the dealer can do that for you too if required.

We thank you for your interest in Cummins products. Please let us know if you need assistance in locating the nearest Cummins-authorized Dealer or Distributor Service Provider. For assistance in locating a Service Provider, feel free to use Cummins North America Dealer Locator, which can be found on Cummins website:
http://www.cummins.com/service_locator/index.cfm

Please let us know if you have other questions and if away from your computer or have a time-critical request that needs more urgent attention, feel free to call us toll-free (from North America) at 1-800-DIESELS (343-7357). Customers may also call Cummins switchboard 1-812-377-5000 (worldwide toll call) and ask for the 800-DIESELS Call Center for assistance.

Email direct: powermaster@cummins.com

Regards,
--
Powermaster
Customer Assistance Center
Cummins, Inc.
Columbus, Indiana, USA





Details:
   Hi,
    I just installed a new dealer purchased cummins thermostat in my
2001 dodge HO diesel.I immediately noticed that my temperature now wanders
between 160 and 195 where with my old thermostat it would pretty much stay
rock steady at 195.Both the dealer and a local cummins shop have verified
it's the correct part #.I did notice that it looked a little different from
my old thermostat(kind of a larger black body on it.I wish I had kept my old
one for troubleshooting.
   Have you guys changed these lately?Will this cause any
problems?Quite a few other people have noticed the same thing on the TDR
site and other webrings.It seems like this thermostat is either wide open or
fully closed.Any clarification would be greatly appreciated. Thank you.

 

Looks like thats the answer to my question about the engine temp. cycling. Thanks.
Now if somebody could figure out what's causing the mysterious "power loss" my problems would all be gone

 

I came across this problem before I changed thermostats. I did notice the P/N change and searched for the old thermostat. You can still find them out there. I replaced mine with the old style and should have bought another one. If I remember, the price is about doubled on the new style. I think it was about 35.00 for the new one.

Mike

 

[quote author=Marine link=board=4;threadid=19486;start=0#msg184237 date=1063468895]
I came across this problem before I changed thermostats. I did notice the P/N change and searched for the old thermostat. You can still find them out there. I replaced mine with the old style and should have bought another one. If I remember, the price is about doubled on the new style. I think it was about 35.00 for the new one.

Mike
[/quote]

Mike wouldn't the new one warm up faster? This seems to be the object that they were intending.

 

[quote author=Haulin in Dixie link=board=4;threadid=19486;start=0#msg184295 date=1063488080]Mike wouldn't the new one warm up faster? This seems to be the object that they were intending.
[/quote]

Yes it would. The old style does take a long time to warm up. I stayed with the old one because I think the constant circulation of coolant is better than an on/off type of circulation that the new one allows. Even if it does take longer to warm up.

 

Any part numbers available for old and new?

The search is on ;D

 

If I get out to the truck today, I will look at the receipt, then I'll post the p/n. This will be the old p/n, and when you give it to the parts guy, he will say, "It looks like it was replaced with blah blah blah." Tell him you don't want blah blah blah, and you want that p/n. He'll say, "They don't make it anymore." You can come back by saying, "Does it show in your computer who has one, because that is the one I want." He'll either be lazy and say he can't get one, or he'll call Cummins and get one for you.

Mike