Skip to main content ↑ ↓
Topic: Fluctuating voltage at cold start (Read 543 times) previous topic - next topic

Fluctuating voltage at cold start

On our last trip we had a number of issues which resulted in replacement alternator and one of the three start battery's ( other checked and rechecked )
On a sub zero morning engine was sluggish and required boost switch to start , as it fired up the volt meter fluctuated between 11v -14v for about 4mins then settled to 14v , started as normal rest of day .
Next morning sub zero and same fluctuating voltage .
It's now in shop and after 2hours of diagnostics they want another 2hours ! Anybody had this problem
Jimmy
2003 U295 3620

Re: Fluctuating voltage at cold start

Reply #1 –
Jimmy,

Are you running any engine preheat (block heater) before starting in the sub-zero conditions?

When to use block heater
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

2000 U320 36' non-slide / WildEBeest Rescue
2003 U320

Re: Fluctuating voltage at cold start

Reply #2 –
Fluctuating voltage is NORMAL in really cold starts, as the INTAKE MANIFOLD HEATER cycles on/off.  And, it is a BIG draw.

And, absolutely, use the block heater if you have shore power for 2 hours or so before starting.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Fluctuating voltage at cold start

Reply #3 –
Great advice , thanks you
Yes I left block heater on overnight , will call garage now
Jimmy
2003 U295 3620

Re: Fluctuating voltage at cold start

Reply #4 –
My guess is also sketchy main ground. I would pull and clean the ground to the chassis and the one to the starter itself.
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: Fluctuating voltage at cold start

Reply #5 –
Easy to diagnose.  Just put a test light or voltmeter on the intake manifold heater and see if voltage drops coincide with the heater turning on and voltage rises with it turning off.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Fluctuating voltage at cold start

Reply #6 –
Brett
You were on the money .
Thank you
Jimmy
2003 U295 3620