Replacing the Petrol Tank in 1938-48 2.5 L Saloons & DHCs

(David) #21

Have a look at the photos I posted under a early item “MK IV fuel tank construction”. There are 2 baffles (running front to back) - one forming the reserve tank section, and the other with small cut outs to allow petrol through the main tank section but limiting the amount of “slushing” when cornering on the road.

As mentioned - the exact positions are revealed by the spot welds on the tank (probably hidden under paint, etc.

(Rob Reilly) #22

That’s it, there are two internal walls so three chambers if you will.
The left chamber is the reserve.
The center and right chambers are the main.

I have drawn in the locations of the two walls.
The left hand wall is sealed all around inside except for 3 holes at the top, so when you fill up, fuel is only able to transfer to the main tank after the reserve is nearly full.
The right hand wall is notched at the lower corners so fuel is free to transfer between the center and right chambers even when you are getting low.

(Peter Scott) #23

That’s really interesting Rob.
Thanks for posting.


(Ron Laurie) #24

Would that explain why the fuel in my reserve tank was old and dirty while the fuel in the main tank was fresh and clean?


(Rob Reilly) #25

Interesting point. In theory when you fill up, the reserve gets filled first, and should mix with the old in there. Then after you get a few gallons in there, it should start spilling over into the main center side, and flow to the right side as well.
Maybe if the fuel in your reserve got really really old, like approaching gummy goo, it would stay at the bottom, and the fresh clean fuel would not mix, but flow over the top into the main side. Just a guess.
It brings another thought, that we should make it a habit to use the reserve once in awhile, and use it up before putting the car into hibernation every winter.

Earlier in this thread I had mentioned the possibility of different tanks.
Here is why.

This is from the 1938 brochure that introduces the 3-1/2 Litre.
Anybody know what this is all about? Is that a '37 tank? Its certainly nothing like my tank.

(Peter Scott) #26

Yes, that’s quite an interesting picture. The chassis looks like a 1937 car but the engine and bellhousing look to be 3.5 litre. A drawing of an early 3.5 litre prototype???

Here’s the 1936 2.5 litre chassis for comparison.


(Rob Reilly) #27

Ah, yes, even though the title says 2-1/2 Litre the engine has the water manifold of the 3-1/2 Litre. I see it has different body mounts than the earlier chassis, and Dunlop “Fort” tires rather than "90"s. So it would seem to be the prototype chassis for the 1938 2-1/2 and 3-1/2 cars, but still with the '37 tank. Perhaps they hadn’t quite worked out the final design of the new fuel tank when this picture was taken, if they were having all sorts of problems with fitting the body panels together.
This picture with the 3-1/2 engine and '37 tank but 2-1/2 Litre title and descriptive paragraph was carried over into the '39, '40 and '46 brochures.

(Ron Laurie) #28

I looked through my spares locker and found this 1938 petrol tank that had been cut open to expose the interior (baffles, etc).-- don’t think it’s a resto candidate. :slight_smile:


(Peter Scott) #29

Hi Ron,

Thanks for posting the photos. It looks as if there is quite a large dip in the middle of the reserve baffle. Does that look original to you, or has it been damaged in some way?


(Rob Reilly) #30

Very interesting, thanks for posting them.
From what I can see inside mine looking into the fill spout with a dentist’s mirror and flashlight, I have three holes about 3/4" diameter at the top center of the reserve-to-main wall.