Bobcat 642b oil pressure light

[Heartland12]

I am just puzzled on my bobcat. The oil light came on so I put in a "y" and added a pressure gauge to see what was going on. I thought the pressure was too low.....but on a cold start the gauge was reading 78psi just above idle and 88 at full throttle. Are these numbers to high? or normal?....would high readings set the light off? I have it out in the woods and don't want to wreck the motor driving it. Any help would be appreciated. I am about 10 hrs in on an oil change with no leaks and oil level good.

 

[OldMachinist]

Sending unit could be going bad or the wire has rubbed and is shorting to ground.
Your pressure readings are high. The relief valve on the oil pump is supposed to open between 57-71 psi. May want to verify the gauge is correct before getting too worried.

 

[Heartland12]

Sending unit could be going bad or the wire has rubbed and is shorting to ground.
Your pressure readings are high. The relief valve on the oil pump is supposed to open between 57-71 psi. May want to verify the gauge is correct before getting too worried.

The gauge I put on was brand new...should I buy another one to check it? If reading are still high is there a way to clean the relief valve spring? Thanks, John

 

[OldMachinist]

The gauge I put on was brand new...should I buy another one to check it? If reading are still high is there a way to clean the relief valve spring? Thanks, John

If you have something else with a gauge on it you can swap it out to see if it reads the same. or you can hook it up to a air line that has a gauge and regulator to see if they read the same.
The relief valve is in the front engine cover. You need to pull the engine and then remove the oil pan to get to the valve.

 

[Rocketrob]

The gauge I put on was brand new...should I buy another one to check it? If reading are still high is there a way to clean the relief valve spring? Thanks, John

Been searching all over for specs on Mitsubishi 4G3 oil pressure. I've got the same issue and am curious to hear how you resolved this? Did you end up finding a faulty pressure gauge, or did you have to pull the engine to replace relieve valve. Thanks

 

[foton]

Been searching all over for specs on Mitsubishi 4G3 oil pressure. I've got the same issue and am curious to hear how you resolved this? Did you end up finding a faulty pressure gauge, or did you have to pull the engine to replace relieve valve. Thanks

take this with a grain of salt , but I would go to a synthetic oil of a lighter weight vs. pulling a engine just to see what happens . So I assume there is no unusual engine noises? Do you think that the engine has been serviced well, not being sledged up , if so a high detergent lighter oil might help clean things some. good luck

 

[Rocketrob]

take this with a grain of salt , but I would go to a synthetic oil of a lighter weight vs. pulling a engine just to see what happens . So I assume there is no unusual engine noises? Do you think that the engine has been serviced well, not being sledged up , if so a high detergent lighter oil might help clean things some. good luck

Still haven't gotten to the bottom of this one, but have discovered a few things: 1. I've verified pressure gauge to be reading correctly, by attaching gauge to known pressure source. And after running the engine for several days this past summer, I definitely get oil leakage around the sender unit and oil filter (no matter how tight I get it). Not a good sign, and I'm afraid something is going to 'blow,' like the oil pump, causing engine damage, or leaving me stranded. 2. I'm supper happy to report, however, that you CAN assess the oil pressure reliever valve (spring, poppet) WITHOUT removing the engine. The oil pan can be dropped and pulled out around the oil intake screen/tub, with no problems. Then the valve can be easily accessed as it's right there in front. Easy Peesy! Note: the back two pan bolts were not accessible with a socket or wretch, but the bolt heads have a Phillips driver as well, so with a short Phillips they can be unscrewed. 3. There was no 'obvious' excessive damage. However here's what I've determined on that. There is a spot of some wear on the poppet with some small scratch marks that can be felt with a finger nail. I'm assuming this could be causing the poppet to 'stick' and not release at proper pressure. I'm not sure if the valve assembly is intended to regulate pressure, or only for excessive pressure release? Anyone know about that? Just the same, the spring, does not appear to be within specs (Free Length 1.850 inches, Pre–load 16 lbs. @ 1.398 inches). I don't have a spring compression tester, but with my 'home-made' job I am getting slightly more pre-load (in the 18-20 lbs) to achieve the 1.4 inches in compression length. Also it measures a bit short for Free Length = 1.702" Soln? I'm hoping I can get replacement from Napa. My understanding is the Mitsubishi 4G3 engine was also used in the Mirage and some of their forklifts. If I could find the part number that could be helpful. Outside of that, I'll have to try polishing the scratches out of the poppet and give that a try.

 

[Rocketrob]

take this with a grain of salt , but I would go to a synthetic oil of a lighter weight vs. pulling a engine just to see what happens . So I assume there is no unusual engine noises? Do you think that the engine has been serviced well, not being sledged up , if so a high detergent lighter oil might help clean things some. good luck

@Foton, To your thoughts of lighter or detergent oil. I did try Marvel Mystery Oil, in hopes of that same idea. Free up a sticky poppet. Did not make any change.

 

[foton]

@Foton, To your thoughts of lighter or detergent oil. I did try Marvel Mystery Oil, in hopes of that same idea. Free up a sticky poppet. Did not make any change.

well how did the inside bottom of the oil pan look, just curious ?

 

[foton]

well how did the inside bottom of the oil pan look, just curious ?

just as a thought have you verified that the correct oil filter for that engine is being used? I have seen cross threaded filters leak . some metric to sae and the other way too, threads are close enough some people just jam them on. of course make sure there is not 2 oil filter gaskets stacked.

 

[Rocketrob]

just as a thought have you verified that the correct oil filter for that engine is being used? I have seen cross threaded filters leak . some metric to sae and the other way too, threads are close enough some people just jam them on. of course make sure there is not 2 oil filter gaskets stacked.

Foton, Yes, I have verified the correct oil filter is being used, and have tested with a new filter. At this point, I am trying to locate the part. No luck so far at local Napa, they've searched and can't find anything. Strange, considering this engine (Mitsubishi 4G32) was used in a variety of vehicles and forklifts, from that era. When I contacted Bobcat Parts, they sent me part number reference for the hydraulic pressure relief. Still waiting to hear back from their follow up reply. If anyone out there has a parts manual for this machine and could get the actual part# that could be helpful. I just have the Service Manual with the picture shown above in this thread.

 

[Rocketrob]

well how did the inside bottom of the oil pan look, just curious ?

The oil pan and supply tube screen all looked normal. Note, I have changed the oil twice, once with MMO to attempt to clear the sticking pressure valve, so I would expect it to look clean. Even when I changed oil before this issue, I didn't notice anything out of the norm. At this point, if I can't find replacement part, I'll be stuck with trying to polish off the mild scratches on the plunger, clean things up and hope for the best.

 

[Rocketrob]

Hi John, Did you ever resolve this issue?

 

[flyerdan]

Hi John, Did you ever resolve this issue?

Rock Auto came up blank for relief valve parts, the Bobcat parts site lists
plunger - 6632742
spring - 6632737
usually one can search bobcat + part number and get results, but not this time.
Perhaps a search of mitsubishi 4g3 oil pressure relief valve will yield something that looks familiar, ebay often has arcane parts available.
Failing that, burnishing the plunger with some scotchbrite discs and coating with a bit of moly grease will probably solve the sticking; I'd be concerned with the bore, as it's in place it will probably be difficult to inspect and burnish it if necessary.