rotten egg smell in engine compartment.

[er9]

i noticed a slight rotten egg smell in engine compartment couple weeks ago when i opened up the cockpit locker and had the engine room opened up. figured it was just marina smell. opened up engine compartment and cockpit locker again today to get some work done and smell it again. dont smell it on deck so im guessing its my batteries.

my two start batteries are behind the engine a foot or two and the water heater behind them. im guessing my batteries might be going bad. they are west marine/ sealed lead acid start batteries. at least 5 years old.

as luck would have it i just filled my heat exchanger with barnacle buster and want to start the engine to flush it out. am i taking a huge risk by even trying to use the batteries once or twice more to start the motor or should i not and just pull them both and replace first?

the batteries are sealed type. i dont see any leaks or bulging near the top of the batteries and they are not hot at all but its been three hours since the charger has been on.

[a64pilot]

If they will start the engine then it’s fine to do so, but it does sound like they are on the way out, and keeping them could cause problems, even with your alternator as well as them overheating severely or leaving you stranded

[er9]

Thanks. Engine compartment will be completely ventilated. Will unplug them when I'm done and replace next time I'm at boat. Guess my electrical upgrades happening sooner rather than later.

[sailorboy1]

I chased a rotten egg odor for years. Turned out it was a VERY small engine seawater leak due to a corroded hose clamp. That sw sits in the line and goes bad and then starts dripping so little you don't even see it.

BTW - was also the reason my engine tach stopped working 10 minutes after starting the engine.

[Cheechako]

Batteries outgas that smell. Check your water though! The more you smell that the more water may be going away.
I would be a bit concerned about ventilation, batteries are supposed to be vented due to the Hydrogen (?) gas.

The other possibility is old hoses and the rotten seawater smell that accumulates in them.

[Ken Pole]

Batteries in the engine space are not really a good idea; heat and probable vibration are not friendly.

[JRSHAW]

Or
If you have recently got fuel at an unknown source, the sulfur content can be very high
Do you have a fuel leak somewhere?

[er9]

Originally Posted by Ken Pole

Batteries in the engine space are not really a good idea; heat and probable vibration are not friendly.

the engine space is one big open space. basically the entire area from the galley bulkhead (companionway) aft to the transom. theres technically no enclosed engine compartment.

i agree though but theres not much space to move them to. on the plus side they are well secured in heavy fiberglass battery boxes.

some time down the road i may relocate the water heater behind them and relocate them to that spot. it would get them about 5ft aft of the engine.

[er9]

Originally Posted by JRSHAW

Or
If you have recently got fuel at an unknown source, the sulfur content can be very high
Do you have a fuel leak somewhere?

havnt gotten fuel in about a year. not that i can see any leaks anywhere but it is an old aluminum tank. ill keep a close eye out for any.

[er9]

Originally Posted by sailorboy1

I chased a rotten egg odor for years. Turned out it was a VERY small engine seawater leak due to a corroded hose clamp. That sw sits in the line and goes bad and then starts dripping so little you don't even see it.

BTW - was also the reason my engine tach stopped working 10 minutes after starting the engine.

interesting, that possibly may be a cause. i replumbed my freshwater cooling system about three months ago. basically i bypassed the water heater in the cooling loop. i couldnt get to the heater to remove the lines properly so i just cut them and left about a 5ft section connected dangling on the floor until i could get to them. i may have to crawl in and properly remove them and see if they smell.

[er9]

Originally Posted by Cheechako

Batteries outgas that smell. Check your water though! The more you smell that the more water may be going away.
I would be a bit concerned about ventilation, batteries are supposed to be vented due to the Hydrogen (?) gas.

The other possibility is old hoses and the rotten seawater smell that accumulates in them.

thanks im gonna charge them again next time im at the boat and keep a close eye on them for smell and heat. i am not using them at the moment until i can determine if they are going bad.

[Siberian Sea]

Hydrogen sulfide gas from batteries

[Little Song]

Hi. Can it be the coolant fluid? I had a similar problem, and the rotten egg smell was due to it.

Cheers.
Jorge

[SaltyMetals]

I agree w Siberian. I doubt you will get hydrogen sulphide being produced by the batteries. It will be sea or fresh water sitting in a dirty location somewhere. I hade a similar problem and discovered it was a small rainwater leak coming down from the cockpit that then drained under the engine but left a little water in the tubes. Some vinegar fixed the smell and some Capt Tolley's Creaping Crack Cure fixed the cockpit leak.
Andrew
"Genial Bee"

[Martkimwat]

Don't know about the US but here in UK you can purchase an inexpensive battery load tester from MachineMart for about £30, will give you some idea if they are on there way out.