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Daniel Wilson
Daniel Wilson,
Category: Medium and Heavy Trucks
Satisfied Customers: 4679
Experience:  Owner at DJ Wilson
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2006 Peterbilt 387 with a cat C15 dual turbo. first off im

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2006 Peterbilt 387 with a cat C15 dual turbo.
first off im new to these big engines.
one of the blue hoses with a valve(the top one theres 2) on the passenger side towards the front of the motor was open and it let coolant into the oil..
so first question is what is that blue line for and which seals in it can possibly go bad to let coolant into the oil?
the truck was driven for 150 miles with water in the oil.
once home, changed the oil, and kept the valve on the blue line closed. (water will not go in the oil again unless the valve is open)
now the truck has low oil pressure, with the oil pressure sensor unplugged after a certain rpm it will start buzzing and eventually put it in reduce power and kill the engine.. if I unplug the sensor, it runs good... I manually tested the oil pressure with a gauge from oreillys and it was 20-25 psi at idle, and didnt move at higher rpms..
what I was thinking what of possibly happened is, the water in the oil caused the main / rod bearings / oil pump (all or 1 of those) to go bad.. to cause low oil pressure..
need to know where exactly does the blue line run, how is that letting water in the oil, and then which test should I run to see why am I having low oil pressure? the engine still sounds great.

Thanks for asking your question. I can help you with this.

Those are heater core hoses. They run from the engine to the cab for the heater. THey can not cause coolant to enter the oil.

If you have coolant in the oil, you have either a failed water pump, cracked or leaking cylinder liner, a leaking head gasket, or a cracked head,

The best way to verify where the coolant is coming from is to drop the oil pan and pressurize the cooling system. You will see where the coolant is coming from.

Please reply back if you need more help or have more questions. I am happy to assist.

Customer: replied 2 months ago.
I never seen water in the oil. I just bought the truck and this is what I was told.. he also sounded like he didnt know much... but he said water got in the oil from one of those valves and when he got back he changed the oil and closed the valve... since then I drove it back and let it idle for a long time and theres still no water in the oil... but there is low oil pressure.

I see. Can you take a picture of the valve and hose? There should not be a valve that allows coolant to enter the oil.

Customer: replied 2 months ago.
One of those. He said the top but no telling..
Yeah those are heater core hoses. The valves can not cause coolant to enter the oil. The valves are just used to shut off coolant flow in the summer.
Customer: replied 2 months ago.
is it possible to cause the water pump seal to leak only when the valve is open? hopefully tommorow ill get with my mechanic and open the valve to verify we are def. getting water in the oil and then go from there.. what do you think about the low oil pressure?
No the operation of the valve can not cause that.
Low oil pressure could be coolant in the oil. Could also be worn rod and main bearings or a weak oil pump
Customer: replied 2 months ago.
how can I determine if its bearings or a weak oil pump? currently have no water in oil and low oil pressure. 20-25 psi, doesnt move even if I go to 1000 rpms which it should be around 60 psi correct?

I like to drop the pan and remove and inspect s few of the rod and main bearings. If they are worn, you will see it. IF they look OK, I would try a new oil pump.

Customer: replied 2 months ago.
is this the correct spot to check for oil pressure? (where I have the small black line screwed in)
that is the correct spot.
Customer: replied 2 months ago.
The 2 blue heater hoses both T off behind the engine and goes to something by the oil filter down the right side of the block. Maybe a oil heater ?? Do not know what it is but that's what he said. And that's what's possibly leading coolant into the oil.. I can send pictures in about 10 min.
Ok. I want to see the pics.
Customer: replied 2 months ago.
2 hoses come out of the cab (heater core) upper hose goes to the upper valve behind the water pump.. the lower one goes to the back passenger side of the block (behind turbo) (as seen in the pictures) oil cooler maybe???? Then it comes out of the block and runs to the rear heater core under the sleeper then goes to the lower valve behind the water pump.
Thanks for the information.
Yes these are heater core hoses. These can not put coolant in the oil.Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 2 months ago.
1 of those heater core hoses are running to the oil cooler once it leaves the heater core.. I'm pretty sure that oil cooler is failing causing coolant to go into the oil.. which means that Heater hose can lead to water going to the oil.. I'm pretty sure that's what's going on..
Most often when an oil cooler fails it puts oil in the coolant. This is due to the oil pressure being higher than the cooling system pressure. You may want to try replacing the oil cooler.
However if you do have a bad oil cooler. The heater core hoses would not have anything to do with that.Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 2 months ago.
How does the heater core hoses have nothing to do with that if 1 of the heater core hoses is running directly from the heater core to the oil cooler..
They only carry coolant to the heater core. They do not cause the oil cooler to fail. The hoses connect to the coolant side of the oil cooler. They do not touch the oil side of the oil cooler. Make since?
Customer: replied 2 months ago.
But if I open the heater core hose valve(the one that runs to the oil cooler) by the water pump then water will go into the oil..
Sir. Trust me. That is not what's happening. All the heater hoses do is uae coolant that's in the water pump and oil cooler. Turning the valve on and off will have no affect on coolant entering the oil.
Customer: replied 2 months ago.
Off of that topic for now.. on the oil pressure question if the bypass valve in the oil filter housing is stuck open can that cause low oil pressure
it can.
Customer: replied 2 months ago.
Well there's is oil steady dripping out of it when I pulled the filter, also I can't move it at all... nothing is suppose to leak out of it correct? And it's suppose to move if working properly??
it will leak oil like that. It's normal.
Customer: replied 2 months ago.
Should you be able to push it up like a normal bypass valve? (Engage the bypass) I cannot move it or anything
No. If you can't move it. It's most likely closed.
Very very seldom do the bypass valves stay open. They open when the oil filters is plugged. Not real common for them to open with nonoil filter restriction.
No. They are very stiff and hard to move. To tough to move by hand.
Customer: replied 2 months ago.
Just pulled the oil pan, what is the procedure to remove the main & rod bearings for inspection to see if this is my oil pressure problem.
I like To drop them one at a time and inspect. If they are the problem they will be severely worn. Don't drop more than 2 mains at a time.
Customer: replied 2 months ago.
Do you have a step by step procedure that you already have written up that you can send me? On removing the main/rods

Sorry. There is not a step by step. I wish there was. You just need to remove one at a time and inspect. The Mains torque back to 190 foot pounds, then turn an additional 120 degrees. The rods torque to 52 foot pounds and then turn an additional 60 degrees.

Customer: replied 2 months ago.
Is this normal wear or is this super worn out?

That looks like normal wear

Customer: replied 2 months ago.
Is it a must change or reusable? Also some thick mud like oil came out of the oil filter.. I'm chasing a low oil pressure problem. Stays at 20-25 psi no matter what even at 1500 rpms, it doesn't change
I would reuse.
Customer: replied 2 months ago.
Anyway to test a oil pump? Oil pump or main bearings is most likely the problem if it's not the rod bearings

NO way to test oil pump. Sorry.

Customer: replied 2 months ago.
Update: main & rods are good. Pulled the valve covers everything looks good other then some milky gunk from when there was water in the oil. And the top was full of oil so the oil pump is working (also took it apart everything looks good...What should I do next?Oil cooler? You said there's no way water can go in the oil from there but if oil can get in the water... and with no oil pressure it seems like the water would over power the oil and go there... keep in mind water never went back In the oil since that valve has been closedWhole reason I opened this question is to find out how water got in the oil and why do I have low oil pressure. I have not solved either which is why I didn't rate your service yet..(keep getting emails)..

Hi Ryan. My name is***** a Cooling system pressure tester with the correct adapter pressurize the cooling system with the oil pan down and inspect for leaks from underneath or through the exhaust manifold ports if you see white ash deposits in the exhaust or had excessive white smoke from coolant burning in the exhaust or combustion chamber. See if it is dripping from a cylinder, the front timing cover area, etc. Let me know

Customer: replied 2 months ago.
Hello Dan, yesterday I pressurized the coolant system up to 20 & nothing dripped down... I'm pretty lost now.. Maybe the guy I got it from fixed the water going into oil problem and been chasing the low oil pressure problem couldn't figure it out so sold it.. and lied to me from the start.. I was thinking maybe it's like a head gasket and only leaks when its hot but I drove it 40 mins. To my shop and idled it for a while and water never went into the oil. the valve covers were caked with milky gunk so there was water Def. In there at one point, weather he fixed the problem or not I have no clue..

The first expert has many years experience as a trainer of Cat engines at the dealer level. I was field service for my local dealer and also have many years experience. coolant in oil is cracked liner flange/head gasket/head crack or liner seals most commonly, water pump, and in rare cases an air compressor failure.

An oil cooler almost always is oil in the cooling system and radiator. So the coolant will be sludge and black in the radiator

Thanks for the update. Hopefully this is not full of block sealer to mask that problem as coolant soaked bearings start a chemical process and eventually lead to a spun bearing.

3406E /C15 engines are known for cracked liner flanges and head gasket failures . There is a procedure for the liner protrusion and spacer plate inspection for the protrusion to be within specs or the result is a head gasket failure or cracked liner flange.

Customer: replied 2 months ago.
I pulled the bearings yesterday too, here is a picture of a rod bearing almost looks like they were just replaced? Also I drained the coolant and no signs of block sealant

Check the backside of the bearing for a part number... See if its a Cat bearing or aftermarket and if its marked STD or oversized

Customer: replied 2 months ago.
Since nothing is leaking right now I think we should go after the oil pressure problem, (idling or giving it gas the oil pressure stays at 20-25 psi doesn't move at all... currently I have the oil pan off, oil pump off, & valve covers off.. no rocker arms are broke, oil is getting to the top of the engine, and the main / rods bearings are good.. there was a little gunk In the oil.filter.. I'm thinking maybe put it all back together with a new oil filter and see if that changed anything? Or what do you think my next steps.should be.. how do I Inspect the liners for Cracks?

On the oil filter housing remove the plugs and inspect the oil bypass valves in the housing for wear, debris, or damage.

If the liner flange is cracked it will leak coolant into the oil and you would loose coolant pressure with the pressure test

Customer: replied 2 months ago.
I will check the bypass valve next.. can I see the plugs on the housing pretty easy or is it something I would need a little more info to do?

using a light look for scuffing or scratch marks on the liners and bar the engine over by hand so you can inspect all cylinders.... Also using a filter cutting tool open up the oil filter and inspect for metal or debris indicating a bearing failure possibly... It is possible you started to spin a bearing... Either rod, Main or possibly a Cam bearing in the head.

You can see the plugs.... They are sealed by o rings. i recommend replacing the o rings

If in the head a bearing could have moved enough to block the oil galley

bearing material found in the oil filter will confirm a bearing failure occurring....

Customer: replied 2 months ago.
Is the bypass valves on oil filter on the side on the housing or inside it where you have to remove the filter to get to them?
Customer: replied 2 months ago.
Is scaring in the oil pump where the inlet & outlet tube go normal? Pictures attached

thanks for the pictures....That is only marks from the o rings for the tube where they have set.

There are two allen head plugs to remove on the filter housing to access the bypass valve.

Customer: replied 2 months ago.
This is what the main bearings look like
Customer: replied 2 months ago.
Update: I put the pan back on, changed the oil and filter & the oil pressure went back up to 60 psi.. so it's back to normal but I have a feeling if you drive it for a while it will dump water in the oil, doubt that problem randomly fixed itself

Thanks for the update. I do not like the look of that last bearing on the shop rag. I see pitting and uneven wear. This can be caused by the chemical process when bearings absorb the coolant and begin washing the bearings resulting in eventually a spun bearing. I doubt the water issue fixed itself either. There is another option if the pressure test is not showing. If this is a small leak or only when things are hot and expanded at running temp a dye leak test might be the next step and then you can pressure test and look from under with a UV light.

Customer: replied 2 months ago.
How do I check the air compressor to see if that's what's leaking water into the oil?

That you could see running down the front timing cover with the pan down and system pressure tested. Not likely but possible...

Customer: replied 2 months ago.
What are these 2 valves for? Are they both for the heater core ? What are the effects if the valves stay closed?
Customer: replied 2 months ago.
Do you have a coolant flow diagram you can send me?

hi Ryan, Sorry for the delay. I help on here in between jobs and was on the road all day today unfortunately. Those are heater core hoses and it does not make a difference. That just shuts off flow to the heater core in the summer months for colder AC in the cab.

I dont believe I do have a flow diagram but I will see if it is in the shop manual once my family is settled in.

Customer: replied 2 months ago.
I cleaned the oil pan & valve covers spotless, shining.. changed oil & filter, after running it for 2 days, the oil looks light and new still kind of then but its.not milky like waters in it, sometimes when I first pull the diptick you can see a few bubbles but hardly any if you wipe it off.and check it.again.. I know a diesel trucks oil turns black 10 miles after you drive it.. could this be because the pan & valve covers are clean?

Thanks for the update. Yes, if you did a thorough cleaning it will take a bit longer for the soot to turn the oil but it will. Keep an eye for coolant. It sounds like so fat it is looking good. Let me know

Customer: replied 1 month ago.
What's the trick to getting this plugins to clip together? Pushing down does not work
Customer: replied 1 month ago.
Never mind, took something on top of it pushing down with superman strength

Hi Ryan, I hope you had a great weekend. I just got your response. The electrical connectors should not take that much force unless there might be a bent or damaged pin or alignment problem. Let me know how you made out.

Customer: replied 1 month ago.
After changing the oil and filter the truck has oil pressure now and runs great.. I been driving it and there's no water going into the oil.. when I got the truck the oil was very gunky because of the water it had in it before and clogged up the filter causing it to have no oil pressure.. Im still confused on how the water got into the oil because it's not happening again and I drove it about 50 miles so far.

Hi Ryan, very odd but good news. Still keep a close eye on it. Its possible the truck was sitting and some of that could have been condensation if not leaks are revealed. Please take a moment and rate my service as that is how the site credits for our time helping on the site..

Daniel Wilson,
Satisfied Customers: 4679
Experience: Owner at DJ Wilson
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