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  #1  
Old 05-09-2016, 11:28 AM
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Dialectric grease on battery terminals; car won't start.

OK, dummy me. Yesterday I noticed the positive battery terminal on the 1984 300DT was corroded. So, I take off the terminals wires and spray battery cleaner along and used a battery post wire brush to clean them up. I then get the bright idea to use dialectric grease to try and prevent further corrosion. BAD MOVE!!! When I realized my mistake, I tried using Simple Green cleaner to remove the dialectric grease. I thought I had removed all of it, but perhaps not.

I've had the car on the battery charger all night; it now shows fully charged. That said, the engine will barely turn over and doesn't spin the engine fast enough to start. Any ideas on what I could use to completely clean the dialectric grease from the battery terminals? Any help is appreciated.




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  #2  
Old 05-09-2016, 11:39 AM
funola's Avatar
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Dielectric grease is not your problem, gotta be something else.
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  #3  
Old 05-09-2016, 11:48 AM
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+1... thousands of users with DG on their terminals... zero issues.

methinks you left a ground cable unhooked...
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My drivers:
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Old 05-09-2016, 12:19 PM
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Remember, voltage does not equal amperage. A shorted cell will still read good with no load on it. Just as a poor connection will show voltage until you try to pull current through it.
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Old 05-09-2016, 12:37 PM
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if you had corrosion on the terminals and cables... you need to pull ALL the cables and clean or replace them. corrosion drastically cuts down on the amperage the cables will pass.

and it'll seriously damage your starter running it on low volts...
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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  #6  
Old 05-09-2016, 02:22 PM
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Get a multimeter (free w/ coupon at HF). That will quickly find the problem. If the terminal connections are a problem, you will measure a significant voltage drop across them. See if you have >10 V across the starter when trying to crank.

I always clean the terminals w/ a round battery brush, connect, then spray everything w/ terminal anti-corrosion (red, at auto parts). That way it doesn't get in the interface, though might not matter. The white stuff you see is lead oxide. That was a common whitener in paint thru the 1960's, until they switched to titanium dioxide. Don't ingest the dust as you clean.
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  #7  
Old 05-09-2016, 04:53 PM
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I took the terminal connectors off and measured just over 13 volts across the battery terminals. I'm thinking the gold plated terminal connector I am using on the positive side may be the problem. I'm headed down to pep boys to buy another terminal to install. I will then measure voltage across the terminals.

BTW, how do I measure voltage getting to the starter? Where do I place the multimeter leads?
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Old 05-09-2016, 07:09 PM
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Are these OEM terminals or the type that cut the cable and use a bolt type clamping plate?

If the latter, those are a very poor design and allows corrosion to go deep into the cable. Corrosion=resistance, which keeps the power from flowing properly.
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Old 05-09-2016, 07:15 PM
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You are far better off finding a donor car and swapping the battery cables from it into your car. Short of that, getting a set of full length cables and installing them is better than putting the stripped wire into a bolt down plate.

The way you measure is place one lead on the starter bolt, and the other lead on the block or intake.
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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  #10  
Old 05-09-2016, 07:31 PM
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OK, I installed the new positive terminal from Pep Boys. Then, a flash of creative thinking came through my brain. I pulled the 1991 560SEL out and pulled up in front of the diesel. I then hooked up jumper cables from the 560SEL to the 300DT. I started the 560SEL and revved the engine a bit. I then tried starting the 300D. It turned over fairly well (before it wouldn't turn over AT ALL) which tells me it may be a shorted cell in the 300D battery.

Question. How can I test for a shorted battery cell in the 300D?
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  #11  
Old 05-09-2016, 07:40 PM
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Here are photos of the new Pep Boys positive battery post splicer. It is really nice! You simply strip off the insulation, push the battery cable into the splicer then tighten with the allen wrench which is supplied.
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Dialectric grease on battery terminals; car won't start.-300d-battery-terminal-004.jpg   Dialectric grease on battery terminals; car won't start.-300d-battery-terminal-006.jpg   Dialectric grease on battery terminals; car won't start.-300d-battery-terminal-009.jpg   Dialectric grease on battery terminals; car won't start.-300d-battery-terminal-010.jpg  
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Old 05-09-2016, 08:13 PM
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Common use these days for dielectric grease is between an electronic component which needs cooling......and the aluminum finned heat sink ... not for connecting items which need electricity to run between them.... my father put regular grease on the battery terminals once.... bad move...


https://en.wikipedia.org/wiki/Silicone_grease

''''Dielectric grease is electrically insulating and does not break down when high voltage is applied.'''
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  #13  
Old 05-09-2016, 08:17 PM
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Quote:
Originally Posted by leathermang View Post
Common use these days for dielectric grease is between an electronic component which needs cooling......and the aluminum finned heat sink ... not for connecting items which need electricity to run between them.... my father put regular grease on the battery terminals once.... bad move...


https://en.wikipedia.org/wiki/Silicone_grease

''''Dielectric grease is electrically insulating and does not break down when high voltage is applied.'''
For sure. I learned the hard way on this project. Take 90% rubbing alcohol to clean the dielectric grease from the battery terminals and connectors.
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  #14  
Old 05-09-2016, 08:19 PM
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Just checked the battery for open cell condition. The fluid floated to the very top of the "green" good (on the line betweeen "green" and white") for five cells and the last cell (#6) tested in the red (not so good). By my math it is 1.275 - 1.26 - 1.5 or open cell on that one cell which means time to replace the battery.

Does anyone know what group size battery for this 1984 300DT? Is it Group 49?

Last edited by HuskyMan; 05-09-2016 at 08:34 PM.
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  #15  
Old 05-09-2016, 08:50 PM
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I've had good luck with the AGM type battery. I think they sell them at Autozoo.

Duralast Platinum/Battery H8-AGM- Read6Reviews onDuralast Platinum #H8-AGM


Yeah, they're pricey but in a diesel you want ALL the cranks you can get!

Group 49.

Do NOT buy a battery from CSK Auto. They're crap and their warranty isn't worth wiping your crack with.

p.s., Electrolyte condition is not a positive indication of a possible short between cells. It's good for an "over-all" condition gauge but the use of a load tester is the only sure way to detect the short.

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