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

(Ron Laurie) #1

The petrol tank in my '39 2.5L DHC is leaking. It has been sent it to the radiator shop to see if it can be repaired, but if not, I will have to replace it. According to the 38-47 Spare Parts Catalogue, it’s the same for '38-39 cars and 46-48 cars, at least for the 2.5 L cars.

Anyone know where I can find one?


(Rob Reilly) #2

Coincidentally, I am stripping the yellow paint off the one from my early '38 car, and I see it has copper rivets and solder joints. It looks like the copper rivets held the pieces together while the solder was applied to finish the joints.
There is some kind of black stuff in there, seems to be a sealant on the wall between the reserve and main tanks. It dripped down into the reserve pickup well. There is some sort of glue on the outside of the well, maybe to seal a leak.
I hope to remove either the well, or the left hand side, to clean it out.
Ron, if yours is the same it can probably be disassembled to fix wherever it has the problem.

(Ed Nantes) #3

The tank shown in Rob’s pics is of a different method on construction to MK IV tanks these were basically two pressing held together by a welded seam around the ‘equator’
I have heard of one owner who dismantled one by grinding/ cutting the seam to separate the halves, then repairs are relatively straigh forward.
The tank in Robs pics seem to share construction methods more related to SS1,SS100,
I found it not difficult to dismantle an SS100 tank which is just soldered together and a few occasional rivets

(Rob Reilly) #4

Thanks for the encouragement; I will proceed with it.
That’s the reason I mentioned mine is an early '38, one of the first 50 cars with the spare tire under the tank, so I thought it might be different from later tanks.

(Ron Laurie) #5

Here’s a photo of my tank.


(Ron Laurie) #6

(Ron Laurie) #7

PS - My car (46166) was built in October 1938 and the tank appears to be identical to Rob’s.


(Rob Reilly) #8

Yes, they appear to be identical.
Ron, does yours have two studs on the forward side?
Anyone know the purpose for them?

(Ron Laurie) #9

Rob, I’ll check on that - the car is 50 miles away from me at On the Road Again Classics in Morgan Hill, Calif.


(David) #10

Had the similar leak problem with mine, and decided to do a repair myself as a could not find a replacement tank as the original. It was mainly pin holes to the petrol filter sumps and one area underside of the tank where to had rested on the felt support pads (I suspect holding water and rust). I stripped all the paintwork, cleaned (inside and out), and made sure it was back to metal and well dry - then used fuel tank grade epoxy putty for initially sealing the holes before checking again for leaks. When dried off I used Slush tank seal inside after sealing off the internal pipe work to the outlets/filters. Then I used 4 layers of Tankguard expoxy paint on the outside. It takes a lot of preparation and work, but it’s going to give the original tank some years of life still. Other problem area was the filters leaking around the brass threads, but solved by used large size O rings and petrol grade non setting pipe thread paste.

(Ed Nantes) #11

When I restored an SS100 petrol tank,I dismantled it[easyas it’s mainly just soldered together. Th welded new sections in where the rust had been, then had all the parts cyanide copper plated. This replaced the coating of the original Ternplate they were made of. And also made the soldering back together easier and more thorough.

(Rob Reilly) #12

Terne plate, that’s interesting, I’ve heard of it but this is my first time working with it. Steel sheet coated with lead and tin to make it easier to solder joints. I see it held up fairly well over most of the outside, but looks like not so well inside, I see rusty surfaces in there.
What a pity they didn’t make it out of brass.

Quite a few dents on the bottom, not at the support pad areas, can’t guess how they got there.
There are two 1/4" threaded studs on the front, in line with the internal walls. They do not line up with anything on the chassis such as tie straps or anything. My guess is they were for attaching to some kind of assembly fixture for holding the parts together while it was soldered.

Looking at this thing, I was reminded of the old joke that a camel is a horse that was designed by a committee. This tank is made of a single sheet wrapped around to form the top, bottom, front and rear, but there are about 25 separate other pieces. That notch on the right front, seems to be no purpose for it. The brake linkage is below it. Likewise the tapered notches at the front corners, the springs are at least 3" below them. Was all that left over from the '36-37 cars?

(Peter Scott) #13

I think the tapers are to permit extreme axle bumps.



(Ed Nantes) #14


Bill had a factory to make money not cars that would have sound petrol tanks 80 years later : >)
I’m not familiar with 1938 tanks, BUt SS100s had 3 captive nuts for attachment points on the front wide of the tank which oddly only attached to sheet aluminium panel. The M IV had 2 straps around the tank with the captive studs on separate brackets from the chassis.
'll have to dig out my 1937 tank and comare it to the pictures.

(Rob Reilly) #15

Yes, I’m sure that’s it, and swaying on turns.
Just musing on the idea of a brass tank. I’ve seen them on pre-WW1 cars. If I had to make one from scratch that’s what I’d do.
The price of the '36 and '37 tanks was 3 pounds 7 and 6. Different part numbers each year and different from the '38 tank. Incidentally all 3 models in '38 used the same 3358/R.1 tank.
There seems to be an awful lot of labor that went into it, regardless of the material. But maybe labor was cheap then. I suppose brass would have added a few pounds to the cost over terne plate, and might have put the sales price of the car over 400 pounds. It was 395.

(Peter Scott) #16

I don’t think the coachbuilt cars had a petrol tank reserve.


(Ed Nantes) #17

They didn’t , except for the SS100.

(Ron Laurie) #18

Anyone got a photo or drawing of the tank interior, e.g., the location of the baffle that separates the main and reserve tanks.


(Rob Reilly) #19

I can see the position of the baffles by the spot welds that hold them to the outer shell. There are two baffles or walls, one about 8" from left end and the other about 12" from the right end.

(Ron Laurie) #20

That’s interesting Rob - two baffles would imply three tanks, but here’s what the Mark IV *'46-'48) Service manual says –

“The petrol tank has two petrol outlets, both of which feed to the petrol tap located on the nearside rear chassis side member. Situated in the petrol tank is a baffle plate offset to the nearside and the two outlet pipes draw one from either side of this baffle When the reserve petrol tap control knob is pushed in, petrol is drawn from the main petrol supply only, that is, the offside of the baffle. When the supply is exhausted and the control knob is pulled out petrol is drawn from the reserve supply, i.e., the nearside of the baffle. The two outlet pipes draw petrol through gauze filters situated in wells in the base of the tank. These filters may be removed for servicing, or the tank may be drained, by unscrewing the brass hexagon caps sealing the wells.”