Sherman fuel tank overflowing
 

We have a puzzling problem with the left hand fuel tank on one of our Shermans overflowing after being driven for a few miles. These are twin diesel M4A2's.

The fuel system is not stock. At some time in the past, it was converted to the two tanks on each side supplying only the engine on their respective side. The supply tubing goes from the bottom of the lower tank to the blower-driven fuel pump (vane type) to a single fuel filter to the injection gallery on the cylinder head.

Return flow is from the return gallery on the cylinder head to high on the upper tank.

Also, there is an interconnecting balance tube running from the bottom of one lower tank to the other to keep the tanks at the same level.

This problem showed up when we filled the fuel tanks on both sides right up.

After driving the tank for a few miles at fairly high speeds to an event, the left hand tank started overflowing badly. It turned out the fuel cap did not seal, so it was switched for the good cap on the other side. This stopped the leakage but the left tank was still found full to the brim after the drive home.

We figured the hose that connects the upper tank to the lower tank was plugged and the return flow to the upper tank could not drain down to the lower one which supplies the fuel. But pulling the hose off showed no signs of blockage either in the hose or in either tank.
That's where it stands. Anyone any idea what could be going on?

Malcolm

Fuel tank issue
 

Malcolm

I have a similar issue when operating my ferret. After sitting for a winter the ferret loses prime in the fuel system so rather than sit and crank the batteries I fitted a small auxiliary tank above the engine bay to get it started. Once it gets going the fuel from the mechanical pump takes over and keeps the ferret running. The fuel tank is above the engine bay hanging on the back of the turret and will quickly overflow with fuel back flowing from the carb under the pressure of the mechanical pump.
My thought is that one of your fuel pumps is too strong and actually pulling from one tank and pushing the back flow into the other rather than through the engine. The cross leveling tube is likely too small to handle the amount of fuel being pushed up.
The trouble shooting tests I would do are-
With the left tank very close to empty, clamp the cross tube off, fill the right tank and start the engines, look into the left fuel tank and see if fuel is bubbling in from the lower (pickup) line.
You could also switch the fuel tank feed lines to the opposite pumps and see if the opposite tank fills up.....

Either way you are driving a working Sherman so good times!

Jon

Hello Malcolm,
It sounds like you have two problems. First, you are drawing from two fuel tanks but only returning to one. And the "balance" tube is not doing what it is supposed to do.
The fuel pump on the 2 stroke Detroit's will move 2-3 times as much fuel as the engine will use, the excess fuel used to cool the injectors, and return to tank. There is a restictor fitting on the end of the fuel rail that keeps pressure between 60-75psi, after that fitting the fuel is supposed to return to the tank it is drawn off. For some reason, both engines are returning to the same side of the fuel system. This has to be a plumbing issue, unless you folks in Oshawa have discovered a way to have a Detroit manufacture fuel!
Personally, I would only use the upper sponson fuel tanks to feed the engines. This keeps the fuel feed line above the fuel pumps. Also, typically there is a primary fuel filter between the tank and fuel pump, and a secondary filter between the pump and injectors.
On a lighter side, I once worked with an old timer who kept calling the Detroit diesels "converters". I asked him why, and he told me because "they convert fuel to noise".

Fuel tank selector
 

The original fuel supply only draws from a single tank and the feed comes from the lower tank on the side selected, using the manual selector on the crew side of the firewall. The fuel selector allows left or right or off. So you must feed from one side to both engines and manually switch to the other tank when the gauge shows "E" (meaning the upper tank is empty) so as to maintain a reserve supply in the lower tank. The fuel not used by the engine is returned to the tank that is supplying the engine NOT to the other tank! The fuel supply rate is 40 gal/hr and at 25 psi.

Now, that's the stock set up.

With your modified set up it appears that unused pressurized fuel from both engines is being returned to the same upper tank and the balance pipe is of too small a size to flow enough fuel to balance the system. If you are going to feed each engine individually then you must send the fuel return to the same supply tank or increase the size of the balance pipe. As your system is still feeding fuel from the respective lower tanks the upper tanks already have a fuel return line fitting it should be a simple task of running a new line from each fuel return fitting on the cylinder head back to its respective upper tank. The existing balance pipe may function (you didn't mention its size) once you are returning fuel to both upper tanks, I suspect it is too small. The lower tank fuel feed is above the level of the pumps so no issue using the lower tanks, gravity is on your side.

Look on page 238 of TM 9-731B and the complete M4A2 fuel system is explained.

The manual can be found here.

http://www.theshermantank.com/downlo...-like-manuals/

I have had experience where although the size of the balance pipe wasn't bad, it was the conglomeration of the fittings on one side of it that caused a restriction, especially considering that the return lines are pumping, and the balance line is simply equalizing gravity.

Hi, I dont know anything about Sherman fueling systems but any fuel tank needs a vent to draw in air as the fuel is drawn out through a fuel pump, would it be your system balance between the two fuel tanks if off because you have a blocked vent, of course your leaking fuel cap will act as a vent on one side.

it would suffice you have a blocked vent on the non overflowing fuel tank perhaps.

just a thought.

Malcolm,

Have you compared the fuel systems between the M4A2s at the museum?

The description and diagram of the fuel system in the Canadian 1950 M4A2E8 Drivers Handbook is significantly different to the description in the US 1943 TM9-731B.

Unfortunately the Canadian diagram is very simple and doesn’t show how the “system of valves” works to return the spill from the side that it is withdrawn.

Is the balance tube that you describe actually the “fuel bypass line”?

Recently I have been attempting to understand the differences between early and late M4A2 systems and it appears that there were many changes during the war. The early manuals are relatively easy to obtain, but I have not yet seen a late manual which thoroughly describes the altered systems.

In 1994, Don Smith’s Sherman was driven approx 30km to Borden for the EME (now RCEME again) 50th parade. During that drive, it ran out of fuel. The left tanks had been partially filled to a level that was considered sufficient for the trip, and only the left fuel valve was on. Upon investigation, it was realized that the excess fuel had been dumping into the right tanks. This may have been due to a similar issue that you are trying to diagnose.

We’re both fuel valves on? Given the 1994 issue, I suspect that your left valve may have been off and that there might be something peculiar about the late fuel system.

All,

Does anyone have access to a late M4A2 manual which thoroughly describes the fuel system?

Colin

Sorry for the rotation of the images. This was my first attempt to post using an iPad. It seems I have encountered the same issue as others.

Colin

Thanks for the comments! When I shake off the flu, I'll respond.
Malcolm

Very interested in the outcome of this thread as we have a tank that does the same thing, returning fuel will fill one tank and the tank the fuel is drawn from will actually run dry, looks like over the years the fuel hoses and valves have been monkeyed with a fair bit. The two lower tanks located on either side of the engine are in place but no longer in use.

John

Sherman
 

the guys at some point put a lot of valves into the system , some at the bottom of the hull , have you checked these?

The tank will be full of gold like that one in the UK. LOL

Detroit Fuel Return
 

Just out of interest for you, the return line restriction port off the injectors, at the end of the fuel return line on these Detroit motors should be about .080 thou, the diameter of the hole to create the correct back pressure for the injectors at full throttle, as the bypass valve will trip at about the 75psi mark. If you view the amount of fuel returning through this hole you will be amazed as to how much force and flow on the return of fuel, it is like a garden hose at full noise! Cheers Andrew.

Here is some information that might aid in diagnosing the problem.

Early M4A2s, and other vehicles with the GM 6046 twin diesels, used a dry sump engine lubrication system. Later GM 6046 engines used a wet sump engine lubrication system. When this change was implemented there were coincident changes to the layout in the engine bay and the fuel system.

The early fuel system routed the fuel supply from the tanks to the engines, and the fuel return from the engines back to the fuel tanks, through one valve assembly. This system only allowed fuel to draw from one set of tanks, and ensured that the spill returned back to the tanks from which the fuel was withdrawn.

The late fuel system used 4 separate valves to control the fuel supply and direct the fuel return. In this system there were 2 control handles in the fighting compartment, one at each outboard side of the bulkhead. Each of these control handles actuated a rod which acted on an equalizer bar, which then controlled the movement of 2 rods. The outboard rod actuated the upper valve which controlled return flow to the set of fuel tanks on that side of the vehicle. The inboard rod actuated the lower valve which controlled the fuel supply from the fuel tanks on that side of the vehicle. So when a control handle is turned to the "on" position it should simultaneously open both the fuel supply and fuel return valves on that side of the vehicle. All 4 of the valves were identical, and all of them were connected to their control rods by means of an "overload" device. The presumed function of this "overload" device is to allow excess movement of the control rod once the valve had reached its limit of travel.

In this late system the operator could supply fuel from, and return spill to, both sets of tanks at the same time. If the operator chose to only open one control handle and therefore only feed from one set of tanks, the opposite engine would receive fuel by means of a bypass tube which connected the engine side of each fuel supply valve. In this instance, the return flow from both engines is returned to the same set of tanks from which it was withdrawn.

The various anecdotes in this thread seem to indicate that this system has proven problematic for current operators of these vehicles. It appears that this 4 valve system has many potential points of failure, and limited access makes diagnosing the issue difficult. My assessment of the potential problems are: Is the control handle able to turn sufficiently to provide full throw to the upper control rod? Are all three pivot points on the equalizer bar free to rotate so that the lower control rods are able to provide full throw to the overload devices? Are the overload devices working properly to transmit the necessary throw to the valve pistons? Are the valves actually capable of the full range of movement from open to closed and does the valve actually seal in the closed position?

When I finally found the diagram of this late fuel system, it brought back a roughly 25 year old memory of being tasked to observe and report if both lower control rods were moving when the left control handle was rotated. My recollection was that my father did not like my answer when I tried to describe what I saw. What I attempted to describe at that time was that when he rotated the control handle, the outboard lower control rod moved slightly then stopped, the equalizer bar then started to rotate allowing the inboard lower control rod to continue moving a significantly greater distance. After attempting to describe my observations and evidently not communicating effectively, we changed positions so that I was inside rotating the handle and he was in the engine compartment observing the movement of the control rods. I do not recall the precise outcome, but suspect that the investigation stopped because both rods where observed to move somewhat and therefore they must be opening and closing the valves. Now that I know that all of the valves are the same (and therefore should have the same throw), and there is an overload device between the control rod and the valve(which could account for some movement of the rod, but no actual movement of the valve), and that there was definitely an issue with fuel returning to the left set of tanks, I strongly suspect that the linkages were actually opening and closing the lower fuel supply valve, but the upper fuel return valve was staying closed.

Provided the fuel system has not been modified, diagnosis of a fault has the potential to be confusing. To use the original example of the left tank overflowing, if all fuel tanks are full and both control handles are on, the overflow condition could be caused either by a stuck closed supply valve on the left tanks (could also be a pinched hose, or clogged in-tank filter), or a stuck closed return valve (or pinched tube etc.) on the right tanks. If the left supply valve was stuck closed, the left engine would draw fuel from the right tanks via the by-pass tube (unknown to the operator) but spill fuel into the left tanks thereby causing the overflow. If the right return valve were stuck closed, supply for each engine would come from the tanks on their respective sides, but the return from both engines would be directed solely to the left tank, again causing an overflow. A third condition could exist which causes an overflow on the left tanks. If the left control handle was intentionally in the closed position because the operator wanted to only use fuel from the right tanks, but the left return valve is stuck open, the left engine would be intentionally drawing fuel from the right tanks, but unintentionally spilling fuel into the left tanks.

Certainly, diagnosis of a fault with a modified fuel system will require a thorough inspection to determine the actual flow pattern and potential points of failure in the modified configuration.

This video gives a few decent shots of the blue painted fuel system components in the cut-away M4A2 (76) HVSS at CWM. If you pause it at 2:25 it gives a good view of the left fuel supply valve. The lower nipple is where the supply hose from the lower left fuel tank should enter the valve. The upper horizontal nipple is where the by-pass tube from the same location on the right supply valve should connect. The by-pass tube can be seen in this image electrical-tied to the starter. The hose from the valve to the fuel pump is in place.

https://www.youtube.com/watch?v=Gc3gZinTJT8


Colin

Malcolm,

In your original description of the problem, you stated that:

"The fuel system is not stock. At some time in the past, it was converted to the two tanks on each side supplying only the engine on their respective side. The supply tubing goes from the bottom of the lower tank to the blower-driven fuel pump (vane type) to a single fuel filter to the injection gallery on the cylinder head. Return flow is from the return gallery on the cylinder head to high on the upper tank." If this description is correct, it would appear that no connection exists between the return lines of the two engines. If true, then your issue cannot relate to a fuel return valve problem.

You also stated: "there is an interconnecting balance tube running from the bottom of one lower tank to the other to keep the tanks at the same level." Where is this connected? Is it into the rear ports on the in-tank filter housing? If so, potentially the left in-tank filter is clogged and the left engine was partially or completely running on fuel cross-feeding from the right tanks.

If your original description of the modified system is correct, it sounds like your issue is that little or no fuel was being drawn from the left tanks, but excess fuel from the left engine was being spilled into them.

Colin