[Jerry]

Yes.

Yes.

OK I’ll quit being cute. Our DD thermostats typically open around 195 and close at 190. If the fan is locked such as when you engage the AC that is where the temps should be cycling.

Normal fan settings are the low speed fan is to engage at 204 and 208 for the high speed.

I would have to look up the temp at which DDEC starts removing power and at what temp DDEC shuts down the engine.

I would try to keep the coach operating in the DDEC fan speed temperature range. All us old(er) farts were used to seeing much lower temps than the coolant temps of today, but our engines perform best and are set up to run at the higher temps.

You can go in and change the fan settings but I think the lower temps would result in loss of mileage and maybe even sooting issues.

[Archived]

I would agree with Jon except that, if your temps are correct, it would appear you have thermostats set at about 178…likely 180. I wonder if the originals have been replaced at some time or are missing or stuck open.

By the way, the cycle in my coach appears (from the temp gauge) to echo Jon’s comments…190-210.

I would want to check why it’s as cold as 178.

[Archived]

Thanks.

I thought, okay Jon I opened the door for you ;-), that higher temperatures wasn’t really for performance or mileage but was to comply with tighter emmission standards.

Joel, help me out. If my temp range is roughly 180-210 wouldn’t the thermostat temperature be close to the top of that range indicating when they open and the lower number in the range suggesting near the point they close?

[Archived]

I do think the tighter emission standards are the reason for the settings on our coach engine computers, but I also believe regardless of if going to a lower temperature creates greater polution or not your engine and its DDEC settings are such that higher operating temps will make it perform better and likely provide better mileage as well.

As to the thermostat I had a clutch failure on a trip a couple of years ago and I had to lock the fan. Never having done that I watched the temps and found my gauge never went beyond a low of 190 or a high of 195. Since the fan was locked the cycling had to be my thermostat. It cost me fuel mileage having the fan locked but without pulling my log book and looking for the record I can’t say how much except to say it was noticeable.

[Ed]

As Jon says, the thermostat should begin to open at about 190 (I think, based on the performance of our coaches) and should be fully open at about 195 allowing complete water flow. BUT, the fan is freewheeling until low speed kicks in at about 204 and hi speed at 208; therefore, there is reduced air flow through the radiator until the coolant temp hits 208. It would probably be possible to lower the fan points to say 196-200 which, in theory, would mean a 10 degree reduction in max temps to 200. If you lowered the fan points to 192-195 (like Jon’s locked up fan, in theory the coolant temps would not exceed 195, as Jon experienced.

Unquestionably, the higher use of the fan would negatively affect fuel mileage and I have no idea what it would do to emissions or the fuel injection mixtures. I would probably try lowering mine to 196-200 IF I knew the whole story of the interactions.

[Bob]

Thanks Joel.

I think I’ll have the fan speeds reprogrammed. Talking to many owners it seems their dash air is on a lot of time, especially for southern coaches. I believe it’s reasonable to think the temperatures experienced with the dash air are okay. I may try 190 for low speed and 195 for high speed.

As for the fuel mileage reduction, I’m sure it’s there. I too had to lock my fan while in the Yukon. I drove 300 miles that way and could really see a difference in mileage. Of course, that’s not a long distance. I have driven a few thousand miles with the dash air on almost the whole time. Even then, I didn’t really see much difference in mileage; maybe a 1/10th of a mile per gallon and that would include both the fan load at high speed and the dash air compressor being on.

Thanks again,

Gil

[Thomas]

I think you’re too low at 190-195; thermostat isn’t even completely open if it’s a 190. I might go 196-200. Who’s doing the reprogramming for you?

[Gerald]

Why? What is being gained? I suspect the engineers that establish the values know what they are doing. Is there information to support the need for lower temps?

BTW, I am not concerned when asking the above about how this impacts the emissions, but I suspect they are impacted.

[Tom]

If the thermostat is 190 degree then that’s the ideal temperature. If that can’t be achieved the low speed fan is kicking in at 204 and high speed at 208 and check engine light at 214 (I think). Changing the programming to 190 and 195 helps the cooling system more quickly meet the engineers goal temperature. BTW, this does nothing to affect nomal cooling fan operation when dash air is on. With dash air on the fan is always in high speed.

I haven’t called my local DD service center yet, but hope they will do the programming.

[Archived]

Can you cite the source for your understanding the thermostat set point is the ideal temperature?

A lot of folks read these forums and it appears to me that when the engineers decided to set the fan speed temperatures there was a basis for the decision. Your statement suggests they were wrong. I would hate to see folks rushing to reprogram fan speeds without there being a sound basis.

[Archived]

The thermostat opening temp only sets the minimum operating temperature at low loads. It is not the “ideal” temperature. In fact, a low thermostat opening temp may increase wear due to closer tolerances between metals and increase buildup of water and acids in oil.

It is a common misconception that lowering the thermostat opening temp or lowering the fan cut-in temp increases cooling capability. Max cooling capability is determined by max radiator coolant flow, max air flow and ambient temps. Putting in a lower temp thermostat or cutting in the fan earlier simply lowers the temperature floor of the engine at low loads. Your oil may not get warm enough to remove water building up acids. You are only changing temps at low load. At high loads the thermostat or the fan cut in temp are irrelevant. They are both fully on anyway.

http://www.tuneruniversity.com/blog/2012/04/low-temp-thermostats-whats-the-advantage/

[Archived]

Jon, I never said or implied the Detroit engineers were wrong.

Detroit states the following: “Coolant temperature normal – 190F”. ThreeGreens needs to understand that we don’t have low speed thermostats and that the thermostat in a Detroit is not to set the low level, but rather it’s to set the normal operating temperature. Clearly, we shouldn’t be running our engines at a lower temperature for any prolonged period. That’s why they say don’t idle the engine because temperatures will fall well short of ideal.

Detroit also states the following: “Thermostats: Start to open – 190F and Fully open – 205F” Fully opened temperatures are typically the maximum temperature in the normal operating range. 190F was the normal operating temperature and it would appear that 205F is the high end of the normal range. The low speed fan kicks in at 204F, another data point suggesting 205F is the high end of the range. The high speed fan kicks in at 208F. I would suggest this should seldom occur, but if it does it’s at the edge of the acceptable rather than normal operating range. Finally, at 214F the check engine light comes on. Hopefully, there’s no argument that this is above the acceptable range for prolonged use.

I stated that I was wanting my low speed fan set at 190F or the normal operating temperature. This will not result in the engine running too cold. It may likely result in more frequent cycling of the thermostat and a nearly undetectacle increase in fuel use. Neither really matter to me. I further stated I’d like to have the high speed fan set to coincide with a fully opened thermostat at 205F. This should simply allow my engine to get back to the acceptacle operating temperature quicker.

Please keep in mind that what I intend on doing or what anyone else intends on doing that changes any factorty setting is not necessarily something others would do. As an example, I changed my transmission programming such that when the jake kicks in the transmission shifts from 6th to 5th not 6th to 4th as was done at the factory. I would rather manually control the down shift rather than have an automatic 6th to 4th at 65mph. Others would rather not take my approach. I would never install manual lockes on an automatic awning, but others might.

I do think the Prevost engineers could have done a bit better, even though they generally did a great job. They should have taken engine temperature into consideration before turning the fan on. With dash air on and running alow speeds under low load conditions the temperature of the engine might well run below 190 degrees.

[Archived]

Gil,

I’m sure you are aware that out engines, the installation and the cooling system are certified by Detroit Diesel. I am sure you are aware Prevost is obligated to meet Detroit’s requirements otherwise Detroit cannot stand behind the engines and provide the engine warranty. I am also sure you are aware despite your opinion about ideal temperature that Prevost did not arbitrarily decide the fan operating temps, regardless of what Detroit might say in their literature.

We are going to have to agree to disagree. Especially your last statement about “I do think the Prevost engineers could have done a bit better……”

[Archived]

Hey Gil,

Drive it and enjoy it, they run fine just the way they are.:)

PS – None of the 4 prior Prevosts I owned were programmed to drop a gear or two with the jake like the plastic machines, always maintained the current gear with manual downshifting to bring on more braking with RPM’s.I now have a retarder and no comparison with a jake, way more better… That’s a redneck term…

[Rick & Denise]

Yep, Jon. We’ll have to agree to disagree. And that’s okay.

I do fully understand the certification process from the OEM.

If I can get my fan start temps reprogrammed. I’ll let you know how it works out. If not, like Tom stated, I’ll just continue to drive and enjoy it.

You come from a manufacuring background, I think. So you likely agree that no one ever produces something that’s perfect. Often it’s better than good and well exceeds their customers’ expectation. Nonetheless, there is almost always room for improvements. Don’t read my statement about Prevost to think I don’t believe they did a better than good job; they did a really good job. I’m driving a Prevost because of that and that their product is far better than anything else I’ve seen.