I was detailing the trunk area of my new (to me) C4S this weekend. My car has a very new looking Interstate battery. It's an MTP-91 (Mega-Tron Plus - 85 Months - 700 CCA). The Interstate dealer says this is a maintenance free battery --- but it's not like an Optima.

I noticed a clear plastic tube coming from the front of the car in the area of the battery. I assume it connected to the original battery in some way to vent it. The Interstate appears to have an oval shaped hole in the center on the top edge which may be for that purpose.

Any information or advice on this? I know Interstate was a popular replacement when I owned a BMW, apparently so for Porsche too. I know with older 911s the trunk liner often became damaged from battery gases, so I want to do the right thing.

Thanks!

 

I could be wrong...but I would suggest checking with Interstate based upon the model# of the battery but it is most likely a sealed mtc. free battery meaning nothing needs to be done.

 

Assuming you have the correct Interstate battery, it has a small oval shaped vent pipe along the top side. The clear vent tube should be connected to the Interstate's vent pipe. Standard "sealed maintenance free" batteries can leak built up corrosive gases. I had no troubles w/my vented Interstate for 4+ years. I recently replaced it w/a sealed (& lighter weight) Optima Red Top which needs no venting. Many here have also gone to the Optima.

 

John,

Dan is correct. The oval battery vent outlet should connect to the clear Tygon tubing that vents into the LH fender well. My replacement Diehard is the same way. Probably the same battery.

As a side note, you can take the rubber grommet and plastic fitting out of the LH inner fender and use them in place of one of the rubber drain nipples in the floor pan, forward near the battery. I was more comfortable having a possible battery vent under the car then into the fender well. It is a two minute change and no new parts required.

 

I think the OEM battery has the vent in a different position than the Interstate battery. When I installed the Interstate battery, it came with a small rubber elbow to connect on the battery and a short hose that connected to the factory vent hose. Maybe whoever installed the battery lost the little bag with the elbow and hose. Call Interstate and they will probably send you the missing vent pieces.

 

I have exactly what you do, and mine wasn't hooked up either. I went to Advance auto and the guy gave me a connector out of his spare parts bin. One end is soft rubber that can be pulled over the vent off the battery (streches over the non circular part) and then the drain line slips easily into the other end.

 

Thanks!
Got one of the elbows from an Interstate dealer this afternoon. Unfortunately my clear vent tube coming from the front isn't long enough to reach it. I'll need to disassemble a little and add more tube or reposition it somehow. Mike mentioned it comes out in the fender well but lit looks like I have to remove the large plastic piece at the front of the trunk to get to the workings of it. Would that be correct?

 

get an optima and then don't worry about it

 

I'm thinking about it....

 

Don't buy a new battery for a connector problem. Great idea Mike, I'll do mine tonight. Remove your spare, under that you will find numerous rubber plugs, remove one of them and stick the grommet and hose from the fender into the hole where the old rubber plug resided on the floorpan of the trunk.

Thanks again Mike.

See you at the Glen.

Andy

 

I just checked mine. The rubber elbow that came with the battery has about 6" of hose molded on. Then a barbed fitting connects the end to the original hose. The elbow and fitting came with the battery. Nothing had to be rerouted or moved. The 6" extention was enough.

 

Andy,

Hi. The vent through the floorpan is better. I hope WG works out for me, I'm afraid I may have to go to Phoenix the Friday before and may not be back till Tuesday.

 

Do you get to where the "plumbing" goes into the fender well by removing the large plastic piece across the front of the trunk?

 

John,

The Tygon tubing from the battery vent is supposed to go to the LH inner fender, right near the little metal ratchet that is the lock down and unlock for the LH headlight assy. There is a plastic 90 degree fitting and rubber grommet that goes throught the inner fender sheetmetal and vents into the fender well, not far from the A/C lines.

You may want to remove the plastic trim in the front of the trunk. Only a couple of screws and it will slide out vertically. This is the piece with that the quarter-turn fasteners that the carpet liner screws in to. Or/or pop the spare tire out. Actually its a good opportunity if you empty out the trunk to do some housekeeping and have a look around.

 

Interstate sells a vent kit for the Porsche (Interstate) battery. I think it is about $6.00.