Switching Fuel Tanks on M936A2

Hi Folks! This question concerns switching between fuel tanks on a 1988 Harsco M936A2 Wrecker. Sometimes, when I switch between the right and left fuel tank (lever under the driver's seat), the fuel system loses prime. I suspect that there is some idiosyncrasy about which I need to learn. Operating these trucks is an art form. You gotta know all kinds of little tricks that are not in the manual. Any suggestions? The truck was just rebuilt at Red River, so I doubt anything is broken. We use this truck daily in our agroforestry business. Thanks!

The o rings in that valve are prone to dry and crack and cause loss of prime. This almost always results in complete loss of prime and not an intermittent problem.

Cool. So, I should disassemble the valve that switches the tanks?

Thanks 98G

Should've asked.... Do you happen to know the size of that O-ring?

The fact that your problem is intermittent makes me wonder if that's the culprit. I'd hold off on pulling it apart just yet.

Sorry, I don't know the o ring size offhand.

Yeh. It's weird. One thing I have learned... I never park the rig on a steep hill with the fuel tanks downhill from the engine. Also, I turn the fuel tank selector valve only when the engine is running and let it idle for a few minutes, before driving. Do you think I am just doing superstitious dances or do these precautions make sense?

Replace all of the rubber fuel hoses. There are a bunch on the fuel tank selector valve.

Try searching "selector valve o-rings".

Here's one to get started, https://www.steelsoldiers.com/showthread.php?76086-5-ton-fuel-tank-selector-valve-cleaning-rebuild

And here one on the fuel lines, https://www.steelsoldiers.com/showthread.php?142270-M931-Fuel-Line-amp-Filter-Replacement-Results

In the past, these have been covered pretty well.

doghead said:

Replace all of the rubber fuel hoses. There are a bunch on the fuel tank selector valve.

Try searching "selector valve o-rings".

Here's one to get started, https://www.steelsoldiers.com/showthread.php?76086-5-ton-fuel-tank-selector-valve-cleaning-rebuild

And here one on the fuel lines, https://www.steelsoldiers.com/showthread.php?142270-M931-Fuel-Line-amp-Filter-Replacement-Results

In the past, these have been covered pretty well.

Click to expand...

I'm with doghead. Usually changing the rubber fuel hoses fixes a lot of fuel problems. There are different grades of fuel line too. Buy the best you can afford for a longer fix!!