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My experiment with runinng 170* thermostats
Just thought I would share what I have found running a lower temp thermostat.
I did regualar coolant maintenace awhile back where I changed coolant filters, took a smaple test with the DD test strips and then swapped out about 5 gallons of DD PowerCool. I had 190* thermostats, no issues with them but wanted to see if I could get the bus to run down the road a lil cooler over the summer months, I never had an over heating issue even pulling heavy in the mountains just wanted to see if it would run about 180-185 instead of 190-95.
With a 170, it runs about the same, maybe even a degree warmer at normal loads going down the road, I figure that the coolant could stand to stay in the radiator a bit longer, the 190 stat may slow the circulation a bit more allowing more time to cool off…it is nearly identical temps anyways. Biggest benefit has been when the fan does kick on and you have heated up the trans fluid with the retarder you can actually cool things off in a BIG way now back down to the low 180s. Similarily when running AC with the fan enagaged you can pull big hills and everything stays under 190* !
All in all I will probably go back to 190s in fall when I do regualar coolant maint. Ideally I guess Detroit…espcially the new ones want them going down the road near 200* for emmisions and fuel economy…the warmer they run (to a point) the better the MPG.
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5 Replies
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It is highly unlikely your thermostat is ever closing once the coach is warm.
Assuming your fan clutch is working and you have not modified the DDEC the engine temps are controlled by DDEC through the activation of the fan. DDEC operates the first stage speed of the fan at about 204 degrees and engages the second speed stage at around 208. If you have a fan clutch failure and you have to lock the fan, electronicaly or using the bolts to secure the tabs to the hub then the thermostat will come into play and cause the engine to run at the thermostat temp.
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Agreed Jon, I think the 170 is not fully open until about 177*, the 190 should operate the same way..going down the road both run at same temps. Only advantage to the 170 has been able to really drop the temps of trans fluid when the fan kicks on either via temp or dash AC use.
BTW the way, the thermostats are an easy change out item and run about $50 or so for the pair if anyone ever needs to replace them!
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Do you have a retarder? Is that why you want to lower the transmission temp?
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Correct, have the retarder and use it alot. Side benefit I see is that when the fan does kick on I am now able to drop temps below 190 on long pulls, hot weather etc, also lower oil temps.
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Your retarder transmission fluid outlet goes into the coolant / Transynd heat exchanger and I believe your DDEC and ATEC are monitoring temperatures.
No matter how much you abuse the use of the retarder the system(s) are going to limit the temp of fluid to 300 degrees. At that point the system will just prevent the retarder from functioning until temps can be held below that limit.
Having said that if you need to use the retarder to such a degree you are running temperatures so excessive you feel the need to re-engineer your coach and install a different thermostat you might want to consider that there are ways as a driver you can use your driving habits alone to effectively limit temps.
I arbitrarily chose to use 230 as an upper limit for my transmission fluid temps. I would anticipate steep downgrades, slow down, gear down and establish a target speed that I controlled using a combination of transmission gear, retarder selector position which I moved up or down to maintain speed, and braking when the speed I selected was going to be exceeded. Driving on the steep grades out west I found it was easy to negotiate an 8% grade for example by gearing down into 4th, considering 55 my upper limit and the 2nd or 3rd positions on the selector were adequate. If the speed did start to creep up past my limit a hard stab on the brakes to get me below 50 kept my speeds down and easily under my 230 degree limit.
I picked that number because that was a marking on the gauge so it was easy to read and my plane had an oil temp limit of 250 so I assumed my conservative limit would extend the life of the Transynd. I still changed it every 4 years however. With my limit I never saw the engine temps affected by the retarder and with the retarder off, letting off the gas pedal brought engine and transmission temps down quickly.
Even if the selector was in the zero position I always left the retarder master switch on and if I had to apply hard braking I never looked at the gauge because stopping to me was far more important than fluid temps.
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