Fuel tank mod

[Grizzly]

would you guys know if you could fit a e36 tank on a 1990 e30?
I've been looking in my area for a tank but I cant find one, and I'm not looking to dish out the 600 bavauto wants....

I've only called a coupple scrap yards and they dont have one, but I know the E36 tank was plastic so I was thinkin in the long run this would be a better swap...

[jlevie]

Anyone have any write ups on this? I would love to do this to my daily. I will do some searches, great thread guys!

A write up on what?

[Airplanecar8]

Anyone have any write ups on this? I would love to do this to my daily. I will do some searches, great thread guys!

peace

[Skafrog]

Jim, this is great info.
Adam Nitti and I have been discussing this mod for a few months now, as he is going through a fuel pump a year currently. The current thought is very sporadic fuel starvation, causing an early pump failure.
Were you seeing these symptoms before switching over?

Thanks,
Rob

[jlevie]

It comes back to me now. It has been forever since I've seen one of those and i had forgotten all about those tanks. Other than a surge tank for the high pressure pump I don't know anything that would help in this case.

[Jean]

I don't know when they changed from one to another, but I've seen both kinds on the early cars. Mine is an 84 318i, and here is what the tank looks like. (coolant from the shitty m10 sprayed under the car/subframe).

[jlevie]

What car do you have? As far as I know all early (through 8/87) cars have a cross over tube between the tank halves.

[Jean]

I have an early tank with no cross-over tube, it only has one hump on the passenger side, now that I think about it, it was closer to 1/4 the tank mark. The filter is recent, and there is no rust. It might be a combination or low fuel and weak pump though... (changing that soon).

[jlevie]

You should not be getting starvation at a half tank. At 1/4, probably. If you are getting starvation at a half, tank either the cross-over tube on an early tank is plugged (probably with rust) or on a later tank the siphon is not as effective as it should be because of reduced flow through the system. That can be caused by a weak pump, rust in the tank clogging the pump inlet screen, or a clogged filter.

[Jean]

Nice fix! At the last autocross with the m30, it was starving for fuel BAD trying to come out of a long corner with 1/2-1/4 of the tank. It fell it on it's face at 4-5k rpm for almost a full second until the car was once again straight....

[jlevie]

Just in case someone else wants to do this there are a few details that aren't visible in the picture.

There is a piece of 3/8" Type L copper tubing soldered into the elbow inside the tank. That tube is bent to roughly follow the siphon tube and curve around the pickup cup in the bottom of the tank. The elbow is threaded into a 2x2x1/8" piece of mild steel that is pop riveted to tank and sealed with JB weld. To adapt the 3/8" copper tube to the roughly 1/2" outlet of the transfer pump I soldered half of a 1/2 barbed coupler to the 3/8" tubing.

Because the later tanks don't have a cross over tube, you need level sensors in both sides. It is a simple matter to graft the connector in place of the connector used for the level sensor on the left side. But the body of the level sensor must be electrically isolated from pump housing for both sensors to work. I accomplished that by using a die grinder to open up opening in the pump housing, insulated the studs with short pieces of heat shrink, and used gasket material above and below the level sensor flange. A hard rubber ring about 3/32" thick around the gage tube and plastic washers work work as well, if not better. If you use a ring, a bit of sealant where it contacts the pump flange would be a good idea.

[makard]

I tried numerous "fixes" before I finally gave-up and bought a fuel cell for the DM cars. Risky to be running at full throttle and fuel starve...terribly lean with that throttle body fully open...can get terribly expensive very quickly!;)

[etxxz]

good point on the return line :p

[gazellebeigem3]

Nice, i do those all the time on e36s, i didnt think to apply it to an e30

[jlevie]

I hadn't though of using the space where the fuel filter normally lives. You might be able to fit a container there that has about a quart of volume. I think that using an externally mounted pump would be better than the complexity and loss of volume that comes from placing the pump in the surge tank.

You'll want to have a return taken off the top of the surge tank that leads back into the fuel tank. Without that the surge tank will air lock.