Bobcat S160 Losing its Prime

[Jim Miller]

I have a 2012 S160 with 140hrs and an Interim Tier 4 engine. It runs fine but, in the last week it seems to be hard to start unless I squeeze the primer bulb a few times. I changed the fuel filter and it made no difference. I've drained the old and new filter and have never seen any water. I've opened the screw on the top of the filter housing to bleed out any air in the fuel line. The Bobcat runs fine once it starts.

What could cause this hard starting?? Does it sound like I have a leak in the line that is letting air in? I can't see any fuel leaks anywhere.

 

[Jim Miller]

I guess my question could apply to any diesel engine. Basically, it seems like a diesel fuel starting problem. I've changed the filter, I've drained the filter (old filter and new filter) and no sign of water, I've lossened the screw and pumped the primer bulb to make sure there's no air in the fuel line. The fuel should be OK since it runs fine once it's started. I can't see any fuel leaks in the line from the tank to the injectors. It seems like the engine just doesn't have any fuel unless I prime it before starting. I think I'm missing something really simple.

I'll really appreciate any thoughs or suggestions!

Thanks!!

 

[Coyote machine]

Does your Bobcat have a gasket/O-ring at your filter housing assembly? If so is it intact, not missing, etc?
If you have a fuel leak it likely would be present on the ground; but to track for one you could wrap and tie a section of a piece of shop cloth/paper towel to any vertical runs of fuel line to catch any fuel that might be missed.

What about your fuel cap? Is it sealing tightly? Could it be contributing to a loss of suction while the engine is being cranked?

Just occurred to me, your fuel pump/lift pump, (if you have one) may be failing to draw fuel while attempting to start the engine, and probably doesn't adversely affect running once the engine starts.

Does it restart if you've been running it for a while without trouble? If so, this could also indicate pump issues.

You mentioned a primer bulb, like on a boat engine? Rubber hand grip bulb? Those often fail on boat engine fuel lines and fail to deliver enough air free fuel to the engine from the filter. Just a place to check, and if that's it use an OEM or better replacement to fix it.

 

[Jim Miller]

Thanks for your reply Coyote Machine. Yes, the fuel filter has a rubber gasket and it was in place with the old filter and a new gasket was on the new filter. Where I park the machine is a clean smooth surface and there is no sign of any kind of leak. I don't know about the fuel lift pump. But, the Bobcat's fuel tank is at the bottom of the machine; below the primer bulb, fuel filter and injectors - so - it would seem that there should be something that pumps the fuel "UP" through the primer bulb, through the fuel pump; to the injectors.

After the engine has run for awhile and I take a break (5 -10 minutes) it will start immediately with no problem at all. If it sits for an hour or more then it won't start unless I squeeze the primer bulb a few times.

The primer bulb is exactly like an outboard motor fuel line bulb.

This whole thing started a few weeks ago when the engine shut down while running and the fuel primer bulb was flat (collapsed) and had to be disconnected from the line to re-inflate. This happened twice within about 10 minutes - but hasn't happened since. (I wasn't present when this happened.) When this happened the machine had about 90 hours and had been operating with no problems at all.

I'm really puzzled about what this could be.

 

[Coyote machine]

Glad to try to help. I'd say primer bulb has failed. When they go flat like that I seem to remember they're done. I suggest asking Google"when fuel primer bulb collapses on my... what is the problem/solution"
I don't have to use my primer bulb oin my boat engines so I don't recall the exact cause/effect which is why I'm referring you to Google or boating sites where the answer will be apparent.

 

[Billrog]

Is the fuel tank venting properly ?

 

[Jim Miller]

OK, tomorrow I will replace the primer bulb and see if that fixes this annoying problem.

Also for Billrog, I'm not ashamed to say I don't know if the fuel tank is venting properly. How can I tell???

I'm sure not too proud to ask for advice and help from you guys!!

 

[HarryN]

When you replace the primer bulb make sure to have it vertical with the arrow on the bulb pointing up.

 

[Coyote machine]

If the fuel tank is plastic type instead of metal it shouldn't squish like the primer bulb is doing, usually the cap has some sort of vent hole to allow air to pass when fuel is being drawn to the injectors so it can flow, otherwise it's like when you use a straw to hold water by placing your finger on top of the straw, after placing the straw in a glass of water and then removing the straw. When you remove your finger air goes in the straw, water comes out the bottom of the straw. Air has to be behind water for it to flow from any container.
A bad fuel tank cap would be less discernable with a metal tank, but the same principles apply.

Try this: Before starting the machine, remove the fuel cap and see if anything changes. If the primer bulb doesn't go flat and the Bobcat starts right up, you likely have a bad fuel cap. If not, and the bulb still collapses then the bulb is more suspect. Also check your tank with a flashlight and make sure nothing is floating that might be occasionally blocking the tank's output hole.

 

[Jim Miller]

OK - long day. Stopped by Bobcat dealer to pickup a new fuel primer bulb this morning. Got to the site and looked closely for any sign of leak and there was none.

I first looked at the green fuel cap and it still looked very new. I formed my lips around the bottom of the cap and I could easily blow air in and out of the cap.

I looked at the original bulb to make sure there were no leaks and that the arrow was pointed toward the filter. I removed the old bulb that was full of fuel. When I squeezed the bulb, fuel shot out of the arrow pointed end.

I drained the fuel filter and no water was seen.

I had a air tank with adjustable output pressure so I blew about 10lbs of pressure into the tank fuel line and I could hear the diesel bubbling and gurgling inside the plastic tank. I could also feel the air coming out of the fuel tank opening.

I installed the new bulb and made sure the arrow was pointing toward the filter. I cracked the air bleed screw on top of the filter housing and squeezed the bulb until the fuel was coming out without any bubbles.

I started the engine, it stumbled and died. Bulb was still round and not flat. I tried again and it started immediately and ran for an hour or so. Left it for about 20 minutes and then started it again with no problems.

I'll let you know if my problem is gone. I sure hope so!!! Thanks for all the help!