Engine/Transmission (1998.5 - 2002) wacky thermostat ?

[dblake]

I changed out my coolant and replaced my thermostat last week with a Cummins p/n 3954194 (190 deg. ) . Soon after I noticed that my temp guage that used to stay pegged on 190 now climbs to 195 then quickly backs off to 160 when the thermostat opens then climbs to 195 again and so on and so on.

I noticed that when I replaced the thermostat it looked a little different than the old one. Kinda more like a bigger black body on it. It seems like my old one liked to partially open to keep it at 190 where this one is either fully closed or fully open. Unfortunately I threw away my old one or I could put it back in for troubleshooting.

Anyone experienced this before or have any ideas?

Thanx a lot!

 

[emarsh]

I sometimes wonder about my thermostat too. I don't drive the truck right now except once every two weeks to keep the batteries charged. Even at 100 degrees outside this thing takes forever to warm up. Makes me think that it never fully closes?

 

[dblake]

This is direct 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: -- email address removed --



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.