Help!!!!!!! Detroit 12v71 oil pressure problems

Hi I hopefully somebody can help me as I'm pulling my hair out now. I have a Detroit diesel v12 71series (2stroke) that I am having oil pressure issues with. I know the pressures on there's engines are not mega high usually. The engine has been rebuilt and 'tested' by a local company a while back and just sat since and going by there sheet the pressures are all fine. All I done to the engine before it was fitted was fitting all the external parts needed. The book says 50-70 psi is normal and 28 minimum at 1800 rpm. Once it is started I only see 1 bar at 1800 and maybe 0.3 bar if I'm lucky at idle so it was shut down straight away. I have tried the obvious like a new gauge-no different. I have replaced the pressure regulator and relief valve in the sump- no different. I dropped the sump again and changed out the pump. Still exactly the same. The gauge shoots up to 5 bar on start up then drops and drops back to one bar. I'm completely puzzled. Any help would be much appreciated thanks

if the gauge shoots up to 5 bar (75psi give or take) the first thought in my mind is that the pump is making adequate flow. The drop back to 1 bar would indicate a leak somewhere, the obvious culprit is the relief valve but you say you have changed that. Is it possible there is a plug missing from an oil passage somewhere towards the end of the line in the lubrication system or does the rocker feed on Detroits have an orifice in it to reduce flow to the top end..? If so that would explain why the pressure initially shoots up then drops again.

That is possibly yes. But like I said the company that rebuilt it have supplied a run up sheet and everything was fine supposedly. I know these engines have individual o rings and fire rings under the head for dealing the bore, coolant and oil. It is possible that one could be leaking but there is no signs of anything coming out externally. I also do know the piston rings are very easily damaged when fitting into the liner. I suppose I should take the manifolds off and check the ports for any signs of oil. I did think this but didn't thing that would cause such a massive loss. If I am to try changing out all the o ring seals the manifolds will need to be removed anyway so I will have a good look

What are the pressures at Low & High Idle given by the rebuilder from the dyno test ..?

1.6 bar @ 600rpm and 4.2 @ 1800. I will have to check again to see what it had flat out. I'd imagine over 4.5 bar when it was up to 2200 rpm.

Do you own or have acceess to an air powered pump ? Plug it into an oil port and turn it on with a gauge connected and see if you caan locate a leak somewhere. Obviously not running at the time.

I can get hold of one yes. Am I right in thinking it would need to fill the whole system including the sump with air before I seen any pressure on the gauge as the air would go through the system and return as if it was going back to the sump?

Wish you were closer to my location I have something that might help, it's called a leak detector that was sold by Federal-Mogul years ago. Actually a couple ways you could make your own. This one is basically a tank that is filled with engine oil and a line off the bottom is connected to the oil galley of the engine then air pressure regulated to say 40 psi (2.8 bar) is connected to the tank. Do this with sump off and look for where the oil leaks the most. Might also be an idea to have valve covers off to see if oil is coming from valve train area.

Another option would be if you have or have access to an air powered oil pump. Connect it to the oil galley and turn it on an again looks for where the major amount of oil is flowing.

Almost impossible to think of all the many places oil could be leaking internally.

I will admit to one mistake many years back on a 12V-71. While rebuilding the oil pump and waiting for the gasket kit to come in I installed the block off plate on the side of the pump finger tight and put the pump on the shelf. Come time to install pump installed it and shimmed the pump for proper gear back lash. Finished assembly and shipped to dealer for run-in on dyno. Came back very low oil pressure. Dropped base and found my mistake, yep never removed cove to install gasket and torque bolts. I think after that if I put a part on temp. I tried to always make it obvious that it was not tight, maybe put tag on it to say what was missing!

No, you use the air powered pump to fill oil into and "pressure" the system. Hook the line up the same place you have your gauge plumbed, and try to fill the system up. That big engine, you're probably going to need a decent sized pump. A pressurized air can isn't going to cut it.

GregD1 said:

Do you own or have acceess to an air powered pump ? Plug it into an oil port and turn it on with a gauge connected and see if you caan locate a leak somewhere. Obviously not running at the time.

Click to expand...

Dang it! GregD1 you beat me to it. I need to type faster!

Grogs123 what you want to do is leave base off and just pressurize the oil system to see where the oil leaks out.

kshansen said:

Wish you were closer to my location I have something that might help, it's called a leak detector that was sold by Federal-Mogul years ago. Actually a couple ways you could make your own. This one is basically a tank that is filled with engine oil and a line off the bottom is connected to the oil galley of the engine then air pressure regulated to say 40 psi (2.8 bar) is connected to the tank. Do this with sump off and look for where the oil leaks the most. Might also be an idea to have valve covers off to see if oil is coming from valve train area.

Another option would be if you have or have access to an air powered oil pump. Connect it to the oil galley and turn it on an again looks for where the major amount of oil is flowing.

Click to expand...

Will the pressure can move enough oil to fill that big engine up?

Dam now Shimmy1 is beating me to the answer!

Cheers for the advice guys! I'm going to get the sump off again tomorrow and see if I can make something up to connect to the port on the bottom of the block where the pump sends the oil rather than through the gauge hole as its only 1/4 npt. Hopefully I will see something. Clearly

Clearly I will be getting oil returning back down but I'm hoping to see it from somewhere I shouldn't. I'm sort of thinking it could be one of the individual o rings under the head. I wouldn't see nothing externally as there is a seal all the way round the block but it could be getting back into where the camshafts sit.

Most of the Detroits had a bypass filter that caused the low pressure at idle, you might check that the restrictor is correct and that you have the correct filter element in it. The original sock filters looked like an elephant tampon....

And keep in mind that Detroits do not carry a lot of oil pressure at idle especially after being warmed up.

old-iron-habit said:

And keep in mind that Detroits do not carry a lot of oil pressure at idle especially after being warmed up.

Click to expand...

True but if it is only showing 1 bar at 1,800 rpm that is only equal to 14.5 psi even for a Detroit that is way low. If this is a rebuilt engine I would be expecting 50 psi at 1,800 or close to it.

Gogs123 said:

Cheers for the advice guys! I'm going to get the sump off again tomorrow and see if I can make something up to connect to the port on the bottom of the block where the pump sends the oil rather than through the gauge hole as its only 1/4 npt. Hopefully I will see something. Clearly

Click to expand...

Before going to a lot of work adapting to the port on the block I'd give it a quick test pushing oil into that 1/4 npt hole. If it is leaking heavy in one spot that should be good enough.

I'm just glad you are not dealing with this problem on a 12V-71 in a Euclid R-35. You need to pull the engine to drop the base!

Would this by chance be a genset application over here most of them run at the 1,800 rpm for 60 Cycle electrical power.

lantraxco said:

Most of the Detroits had a bypass filter that caused the low pressure at idle, you might check that the restrictor is correct and that you have the correct filter element in it. The original sock filters looked like an elephant tampon....

Click to expand...

lantraxco, I'm glad I was not drinking coffee when I read that one!

I've been racking my brain on this one. I have many 12V71 rebuilds under my belt, (Wabco and Terex scrapers mostly) Never had an issue like this. Obviously you are using the same oil you have always used? Need to know how many original components were switched from the original engine. Do you have remote mounted full flow oil filters, etc. ? Something has happened since the Dyno test and installation of the rebuilt engine. Also, the oil supply to the cylinder heads shares a seal ring with the cooling system, so if that seal was leaking you would most likely have oil in the coolant.