MPG at 80 MPH sucks anyway
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| Additional Tranny Cooler. Thermostat required? http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=27848 |
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| Author: | Bill.Barg [ Sun Dec 23, 2007 1:08 am ] |
| Post subject: | Additional Tranny Cooler. Thermostat required? |
Is it required to use a thermostat when adding a tranny cooler or does the 545RFE transmission have a thermostat that regulates fluid flow to the stock cooler during cold operation? |
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| Author: | litton [ Sun Dec 23, 2007 10:18 am ] |
| Post subject: | Re: Additional Tranny Cooler. Thermostat required? |
Bill.Barg wrote: Is it required to use a thermostat when adding a tranny cooler or does the 545RFE transmission have a thermostat that regulates fluid flow to the stock cooler during cold operation?
Can't help you with your question but I am curious why you need an additioal cooler? |
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| Author: | Bill.Barg [ Sun Dec 23, 2007 8:50 pm ] |
| Post subject: | Why a tranny cooler? |
In Arizona, the daytime temps on I-10 are easily 100+ for half of the year. At 80 mph I have found that the manifold air temps are really high. I think this is because the tranny shares a radiator with the air conditioning and is stacked in front of the intercooler. I believe this high temp air effects the way the ECM contols the fuel pressures, via the MAP, in a way that effects efficiency. My anecdoatal evidence is crappy fuel economy at high speeds in very hot weather. I, and others have found that the EVIC will read good mileage for the first part of a desert trip... maybe the first hour, then go down by 5 mpg. I think that this is evidence of some temperature limit that the ECM uses to change fuel delivery. (now that I say this, the fuel is probably getting pretty warm after an hour, and will have an effect to (see fuel cooler topics)). Also, it is very noticeable, the point at which the engine water temperature exceeds 190 F and the dash gauge startes to read 3/4 of the max value. I think this is because the engine water radiator, and tranny cooler/AC radiator, and the intercooler are stacked 6 inches thick, and even with the belt driven fan / electric fan combo, heat is just not desipated well enough to give the best performance. I believe that the tranny fluid reaches a temperature where the tranny computer instructs the engine computer to scale back power output. I am not sure, but I think it might inhibit the TC lockup as well at high tranny temps. I dont want to get that point when I am towing a 3000 lb load next summer. I have found the AC to really effect milage. I think that part of this is because the AC has to work very hard dumping heat at the high temps caused by the tranny cooler it shares. If I can get the AC to be more efficient, i can improve mileage, in the summer. Experts.. please inform where I err in this point of view |
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| Author: | gmctd [ Sun Dec 23, 2007 9:47 pm ] |
| Post subject: | |
I didn't see anything to indicate that function, but ECM does use the Inlet Fuel Temp sensor to modify 545 pressures, shift ranges, and TCC lockup - fewer gears the colder it gets. However, B&M and Hayden and DeRaille offer temperature-controlled bypass valves for external cooler applications. |
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| Author: | Joe Romas [ Mon Dec 24, 2007 10:15 am ] |
| Post subject: | |
Just as a FYI. Transmission fluid temperature is a hot topic on another board I read (ev-update@yahoo). On the EV, VW's Eurovan, they use a very crude cooler mounted on top of the tranny and a good percentage of the trannies fail. It seems that once the fluide gets over 220f it degrades rapidly in just a few k miles. But if it never sees those temperatures will last well over 100k miles. Merry Christmas to all. Joe |
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| Author: | litton [ Mon Dec 24, 2007 10:18 am ] |
| Post subject: | |
I also live in AZ but have seen no problem with the tranny in the high temps. My GC has the same unit behind the HEMI and I use it to tow my 6,000 lb TT with no problems in any temp. The 545 does have internal temp sensors that cause it to downshift to a lower gear above some upper limit. Apperantly the increased pump output aids cooling by sending more fluid through the cooder. Unlocking the TC would actually cause tranny temps to increase so I doubt it does that. |
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| Author: | DarbyWalters [ Mon Dec 24, 2007 10:38 am ] |
| Post subject: | |
MPG at 80 MPH sucks anyway
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| Author: | litton [ Mon Dec 24, 2007 1:26 pm ] |
| Post subject: | |
DarbyWalters wrote: MPG at 80 MPH sucks anyway
Actually, here in Zonie land, the unofficial speed limit seem to be 84!!! and the CRD has a tough time getting over 25 mpg at that speed. However, beware of the 90 year olds driving full size Buicks and Crown Vics at 90....., or 45......either way pass with care. |
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| Author: | AZScout [ Mon Dec 24, 2007 2:46 pm ] |
| Post subject: | |
I've always had the overheating problems here in AZ, especially with the AC. All that I notice is that my mileage for city and hwy are the same, but that probably has more to do with tires, lift, etc. I do know that once the intercooler is swamped, the power definitely decreases. This was verified with a dyno. This beast needs extra cooling and space is at a premium... |
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