Is it possible that a battery tender causes electrolysis problems enough to create a radiator pinhole? dealer says it creates a voltage in the coolant even though the charger is connected to the battery poles.

Say what?!? The output of the battery tender is 5 amps max in the charge stage. In the maintenance phase of the battery tender the amps are in the .5 to 1 amp range. Your alternator puts out 55 to 115 depending on model. The amperage is going to the same place with both. I use and have used these tenders in both 12 and 24 volt models for about 4 years on approx 300 + items of equipment. I have also used this on my 90 300E for extended periods of deployment (7 months) with zero problems. Sounds to me that someone has used the wrong coolant and/or the wrong cap. Just my experience of many years of batteries and chargers.
Chris

I thought so too. Dealer just wants to weasel out of a warranty claim.

A) Thats BS
B) So what if it did create a voltage. How does that create a pinhole.

J. Roncallo

Look at the radiator mount design. Brass or aluminum radiators are mounted in rubber isolators or other non-conductive manner, so they are electrically isolated from the body and engine and the rubber in/out hoses are also insulators.

Mounting a modern aluminim matrix/plastic side tank radiator by the side tanks also electrically isolates the radiator from the rest of the car since plastic is an insulator.

Electrical isolation mounting prevents radiators from combining with engine castings - either iron or non-ferrous materials - from developing and anode-cathode relationship in the presence of an electrolyte - the coolant.

As stated, the claim that a battery tender could hole a radiator due to electrolytic corrosion is pure, unaldultered BS!

Duke