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Update: '98 Magna with Detroit Diesel 40E Overheating

Yahoo Message Number: 63536
Many thanks to those of you who offered input for the overheating problem on our recently purchased 1998 Magna w/Detroit Diesel Series 40E.
Just wanted to let you all know that we had a successful mountain-climb-test-drive today in 95+ degree heat on a 6% grade between Phoenix and Prescott, AZ.

We're attributing our success to the following:

A new thermostat.

Cooling system flush and refill.

Reconnection of the electronic controller board in the hydraulic system that causes the radiator fan to switch to "full speed" when the A/C is turned on. Disconnection of this board was causing the fan to run on "full" at all times, robbing the engine of about 25HP (or so) when full fan speed was not required. The controller board had probably been disconnected because the relay in the steering compartment to trigger it had been wired incorrectly.
A dedicated ground wire from the water temperature gauge to the chassis fixed an issue with the gauge reading 20 to 30 degrees too high. It was difficult to interpret what was happening with the engine temps due to the loss of granularity when temps were reading above 230. (I.E. the distance between the degree markings on the gauge are greater and therefore easier to read at "normal" temps and become very squished together in the 230 to 250 range). With the new dedicated ground wire temps are reading within 4 degrees of actual.
Finally, manually downshifting on the steepest parts of the climb to ensure that the engine was operating in the sweetest part of the power curve. Hopefully, once we're free of Phoenix summer temps (High of 108 today) combined with having to climb out of the valley, we'll be able let the Allison do its thing without intervention.
Time to head back to Michigan, get our stuff, and start this full-time RV thing in earnest!

Cheers,

Scott & Susan Ueland
1998 Magna 36' #5587

Re: Update: '98 Magna with Detroit Diesel 40E Overheating

Reply #1 –
Yahoo Message Number: 63553
SCott & Susan:

Great news. Good for you. Enjoy your travels.
Tom Dunlap
2000 Affinity

Re: Update: '98 Magna with Detroit Diesel 40E Overheating

Reply #2 –
Yahoo Message Number: 63560
Scott & Susan

Ok you mention that when you get out of the high phoenix heat you hope that you can let the transmission do its thing. Not so. I'm not familiar with your engine. . But when you start up a grade and your engine starts to go below a certain rpm, you will notice your engine temp. to start to climb. You need to shift down and raise the engine rpm up. This allows the coolant to circulate and keep the temps. down.

Good luck with your full timing.

Bo Lee

2000 Magna #5896 385 Cat

Re: Update: '98 Magna with Detroit Diesel 40E Overheating

Reply #3 –
Yahoo Message Number: 63562
Scott & Susan- If you continue to experience overheating, try a new radiator cap. If that's not sealing to the proper pressure level, it will allow coolant to steam off and the engine to overheat even when all else is proper. Mike

Re: Update: '98 Magna with Detroit Diesel 40E Overheating

Reply #4 –
Yahoo Message Number: 63596
Glad you got you problem fixed! Over 40 years wotking on Gas and Diesel engines cooling system problems have been tricky! BTW we are at the moment in Verde Vally Az. on our way to Yuma! My little 330 so far running cool. Had a nice climb from Show Low to here. Good luck and thanks for sharing! Ken 99 Alluere 30356.