Thread: Expansion Tank with Low Level Sensor (BMW)

What model bmw is that off?

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I thought the BMW tank although very similar does not have one of the small outlets on the bottom. There will be a few old threads about this. I still wonder why more dont fit the $2 ebay sender to the original tank as I have done 4 times now with great success..

From memory the BMW sender is closed circuit when level is high and open when level low so you will have to wire in a 5 pin relay to set off any alarm when level drops

Originally Posted by benji

What model bmw is that off?

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Quite a few e30 e36, see the bottom of this listing, 86 variants

BMW E30 Radiator Expansion Tank Facelift 320 325 316 318 | eBay

Originally Posted by Rage Over

I really want to put a different hose on it as I fear that bracket cutting into it but it's not as bad as it looks in the photo.

You my as well remove that bracket seeing as it's not supporting the brake pipe anyway.

Originally Posted by wayneg

From memory the BMW sender is closed circuit when level is high and open when level low so you will have to wire in a 5 pin relay to set off any alarm when level drops

The level sensor from the early injected Classics fits the bottle too. I haven't investigated which way they operate yet though.

Originally Posted by wayneg

I thought the BMW tank although very similar does not have one of the small outlets on the bottom. There will be a few old threads about this.

Yes, I wrote about that recently. I'll take a couple of side-by-side photographs on the weekend so people can see the exact difference. The only missing connection (actually an inlet) is the tiny connection at the bottom that runs from the throttle body heater, which I have deleted.

For anyone interested, read from this post onwards:
Which heater core

I might add that information to the first post tonight if I have the time.

Originally Posted by wayneg

I still wonder why more dont fit the $2 ebay sender to the original tank as I have done 4 times now with great success..

Probably for the reason that you have replaced it four times... Joking, of course! I'm guessing they were four different installs, not replacements.

That works too, however it is potentially not as reliable (anecdotal evidence to the contrary aside). I normally go for the most do it yourself option using the most available low-cost option however this was one of the few items I don't want compromise on (says I with the dodgy-looking hose).

Originally Posted by wayneg

From memory the BMW sender is closed circuit when level is high and open when level low so you will have to wire in a 5 pin relay to set off any alarm when level drops

That's nothing that can't be fixed with just a transistor. It just depends on what you're signalling. An LED or two or an alarm wouldn't have any problem with a transistor rather than a relay.

Originally Posted by Scouse

You my as well remove that bracket seeing as it's not supporting the brake pipe anyway.

It supports the throttle cable. I pulled it off for the photograph but it could still be removed. The cable doesn't need the support there.

Rage Over, I would have serious reservations about removing the hose from the block to the bottom of the expansion tank. There is quite a heavy flow through there and its a high point on the engine. No problem deleting the the throttle body, I have routed mine direct from the block to the expansion tank with new hose. The hard plastic stuff goes brittle. I would also recommend removing the surplus hose clamp that is still on close to the tank on your car.
I have fitted the senders to 4 separate cars. The 1st one I did was not a great success as I dropped the whole sender into the coolant not wanting to drill a 12mm hole in the tank. I kept getting false warnings. I eventually did it correctly and have had no issues at all. What I think is the best selling point is the sender is 10mm lower than the level. The smallest problem shows before any dramatic outcome.

I picked up an expansion tank from a diesel discovery that doesn't have the block feed nipple on its underside. I've modded it to accept a level sensor, and want to add a temp probe before I fit it.

I too was going to do away with the hose from the block to the tanks underside. Instead I was going to fit a manual pressure relief valve on a short length of hose. This would allow me to release trapped air. But now its been mentioned, should I be concerned about a "dead spot" of coolant flow, if I block this hose off, leading to a localised hot spot.

I guess using one of the laser heat guns would tell me if there was a localised overheating problem.