(2) GROUP 31 HD VS (2) 8D's

[BUS COMMANDER]

I have a GN 4106 and having battery issues. The age of the (2) 8d's dictate the need to replace them. Has anyone out there replaced their 8d's with the 31 HD"S? Are they enough to start the Detroit 8v71? Any response will be appreciated.

Thanks

Wes Jackson

[daddyoften]

I've been starting mine with 2 tired 31's but can't compare it to 2 8d's. Mine is still a work in progress but I would like a better answer my self.
Eric

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[buswarrior]

like everything... it depends.

Yes, it will work when it is warm.

Yes, it will work in the cold if you have a proper way of pre-warming the engine.

You might have trouble if you try to keep the big blowers going in stop and go traffic when the alternator can't make what you are consuming.

You will have trouble starting a cold engine, triple trouble in winter conditions: engine doesn't like to turn cold, battery capacity lower due to temperature, engine requires strong turn to heat colder air to combustion temperature.

Weight savings, cost savings, oh my aching back savings...

How cold do you ever expect to have to start it?

happy coaching!
buswarrior

[chessie4905]

Usually an 8v71 will start in 1 revolution or less, providing it is not in poor condition. 2 group 31 would start it in temps above 50 degrees. HOWEVER, if it is pretty cold, you are trying to start it after replacing fuel filters or extended cranking from an engine in poor condition, then all bets are off. Better on the 8 DS with the added insurance, but you will save money on the smaller batteries, unless you need to modify the cables to connect them. Your call.

[Lin]

We switched from 8d's to group 31's about three years ago and have had no issues.  I can not even tell the difference.  However, we do use a block heater if we plan to start in the cold.  It was my understanding that the original design used 8d's to allow the bus full of passengers to idle for long periods with the AC or heat running though.

[TomC]

I too changed my 2-8D's to 2-Interstate 31's with 950cca per battery. They crank my 8V-71 just fine (12v starter). For cold, I usually put my 300 watt halogen work light below the crankcase the night before to warm up the engine. If not, I have started the bus down to 17 degrees alright. If I do have a problem I have a jumper relay that jumps the 2-8D deep cycles to help out. I have started the bus this way when the starter batteries died one time. By all means, change to the size 31 batteries-plus virtually all trucks and many buses are using 31's now. Good Luck, TomC

[kyle4501]

You will need to check the amp hour ratings, but you will likely need at least 3 G31's to replace the 2 8D's.

Also, low voltage from insufficient batteries will shorten the useful starter life.

Someone had put 4D's in mine. They checked good, but I wanted my coach & house batteries to match, so I replaced them all with 8D's. It starts so much better now.

Good luck!

[OneLapper]

Three group 31s are close to the same capacity of 2 Ds. 

[luvrbus]

Eagle used 3 group 31 on their passenger bus with factory AC 2-8D's for AC is a old wife's tale they were for reserve for starting.In cold climates Eagle used 4-G31 same as the buses of today use for batteries.No way would I trust 2 -G31 batteries without a backup plan JMO    

[pabusnut]

I have been using 2 group 31's for about 8 years, and never a problem,---except when I left the lights on!

My backup plan involves AutoZone or Wal Mart! 

Steve

[Cary and Don]

We have been using a pair of 4Ds in our Neoplan 8V92T. It spins it just fine. They are a lot smaller than the 8Ds.

Cary