My '93 is on its third Cummins thermostat in 1 year. The problem is that after a couple months they wont hold a steady temperature anymore. I did some reading and saw that a few people have cut out the jiggle pins and have cured the problem. Has anybody here tried this? I also have a spare non i/c thermostat to play with too. Will it fit my i/c engine?

 

In the good old days, a thermostat would do a fair job regulating coolant flow through the radiator giving you a relatively stable temperature. They are not that good anymore, non of them. Now they are more like opened or closed giving you that annoying swing on the gauge. Removing the jiggle pin and/or drilling a bigger hole in the thermostat doesn't help you that much. All you have accomplished is diverted a fixed amount of coolant to the radiator, which yes raises the temperature in the radiator at the expense of the temperature in the block. Best option is to reduce the airflow through the radiator allowing it to hold some heat.

 

I blocked off half of it and it seems to keep the temperature more stable. My main concern is the head cracking due to the extreme temp swing.

 

I got the same deal going on with the Cummins thermostat in my 91, it replaced a good working el-cheapo parts store unit, but I had the head off and figured I would use a Cummins thermostat....nope. Gonna put the el-cheapo back in, as it never had the temperature swings the Cummins unit has...

 

The initial temperature swings on both my trucks was rather dramatic, even when it wasn't cold outside. After that, the swings weren't significant enough for me to worry about the head cracking. It is just annoying. I made a grill cover for my 91 from a canvas tarp and plumbers strap. Worked great.

 

I'm going to install a real water temp gauge when I get a chance. The big swing on the gauge might not be as scary as it looks. I'll post an update when I get it done.

 

Most of the time if your experiencing a dramatic swing on the temp gauge it because you have either the wrong t-stat installed, or the correct stat installed incorrectly.
The cummins stat has 2 jingle pins, compared to most aftermarket stats that have 1. This is to allow for sufficient coolant to flow while the stat is closed to prevent engine damage. The stat is designed to open and close in order
To keep the engine operating on it's designed range and the two pin design facilitates this.
However if the pins are not installed on the proper alignment the casting of the block pushes them shut, not allowing much if any ow until the stat opens. Then you get a flood of cold coolant , resulting in that huge temp swing, which tells the stat to close again and so on and so on

The correct jingle pin alignment was deemed important enough for its own TSB .
A winter front is the best way to invrease heat without risking your block
I alwYs found a pizza box worked well....,
Hope this helps,
Chris

 

Got a TSB number?

 

If it's not in the write-up in the stickey, prob not.
That was a few years ago I had that, but they had it on hand at the Cummins shop here at the time.
Ive got to do a t-stat on my 04 sometime soon, so I'll ask for the number while Im there..may be a few weeks yet tho.... Im pretty good at procrastinating..

 

Here is a tsb about the t-stat...Mark

 

Mark, thats close, but for the 2nd gens, none of my 1st gens had the bypass hose.
Ill see if I cant find it next time Im at the shop

 

Thank you sir!

 

I remembered a Service Bulletin about gauge fluctuation being normal and expected with the updated thermostat for the 2nd gen trucks. I've always installed this thermostat in these trucks, they've always caused gauge fluctuation, and I've never worried about it or seen it cause trouble. Here's the bulletin:
http://dodgeram.info/tsb/1994/07-07-94.htm