RB25DET is burning oil

[eric240sx]

RB25DET is burning oil

What's up, I am having trouble diagnosing what is causing my rb25det to burn oil. The engine is in a 240sx RHD, the following are the most critical parts of my setup:

Great condition GTX3076R Garrett Turbo, new 740cc injectors, new head gasket,

Fully built valves, new top mount manifold, new coolant/oil lines, 

new pistons, bored cylinders, 44mm wastegate, recirculating bov

Deleted pcv system due to the rb26det valve cover conversion but I am atmospherically venting from the valve cover 

Oil weight is 10w-30 synthetic 

 

The car was running fine 6 months ago when I got the engine finally running but now it starts smoking as soon as I start it, cold or hot, the piece of misery will start smoking blue smoke. It will smoke as you start it, as you idle, as you accelerate, and especially if you rev it high. There is no oil in the turbo inlet. Please help me figure this out, thanks!

 

[KiwiRS4T]

How many KM since rebuild? Has head been planed - checked for straightness? correctly torqued?  rings properly bedded in? Got  a new oil pump? Any oil restrictors fitted? Returns bored out?

If you run out of ideas do a compression test and or leakdown test and then  pull the head off - examine the gasket, check the head and block (maybe get the head crack tested) - check the bores to see if they are glazed.

[eric240sx]

The engine went through a full rebuilt 6 months ago and was mostly just dailing it and did some racing on the street and about one racing event. I'd say probably about 8k km, just to be safe. I put in new pistons and full heavy duty Tomei valve job. The car does have a new oil pump and an oil restrictor on the turbo, I believe it's a 30th thousand and the head gasket on right now is a 1.5 cosworth gasket 

ill do a compression test today and see what results I get 

[Trex]

ring gap?

[eric240sx]

I feel like it might be the piston rings, which is a bad thing for me becuse I have never replaced pistons rings and I don't want to pay over $1,500 to have it done by a shop 

I'll do a compression test and start isolating out factors that can't play a role so I can really diagnose the problem 

At first, I thought it was a bad turbo seal, that's why I changed my setup but it's still doing it 

The block I have looks healthy and straight but hasn't been tested for cracks, but it was running fine for 6 months, we'll see what happens with the test, I'll do a dry and wet test 

[eric240sx]

I did the compression test and got anywhere from 45psi to a max of 75psi... did I do the compression incorrectly? How do you guys do it?

[vxsr33]

Remove spark plugs, unplug CAS, put comp tester in cylinder and crank over around 5 times, repeat for each cylinder.

Next put a few drops of oil in each cylinder and repeat the comp test. If the readings are higher when the oil is put in its most likely piston rings.

45 - 75 psi sounds extremely low.

[eric240sx]

The engine compression is already lower because of the 1.5 cosworth head gasket its running on.  When I bought the engine and finished the rebuilt, it was reading 120psi with the thicker head gasket and life was great. I did a full engine rebuilt, it saddens me how its already having problems 6 months later. Hopefully I just installed the piston rings wrong.

I will be performing the compression test again tomorrow and then with the wet technique and I will let you guys know what I get

thank you for the help so far!

oh, and i also doubt it can be cylinder deformation because i read online that the engine wouldn't even run if it was and my engine starts right up and idles normally, its just burning oil on start, idle, and rev

[Trex]

On the bright side; it's now setup perfectly for more boost and nitrous

[eric240sx]

1 hour ago, Trex said:

On the bright side; it's now setup perfectly for more boost and nitrous

You're right! As soon as I isolate the problem and fix it where it doesn't burn oil anymore, I will be so happy. Afterall, I'm only 16 years old who worked in the fields to afford this 15k project all by myself. Which is why I feel disappointed and frustrated that only 6 months after the built the engine started burning oil. 

When having new piston rings, do you need to keep the engine in high RPM or low?

[eric240sx]

I took this picture yesterday when i did the compression test. Left to right is spark plug #1 to spark plug #6. Then the coils correspond to the spark plug beneath. The coil-pack very above is for spark plug #6

Spark plug 3 i broke when removing but i replaced all of them with new ones 

[Kinks]

9 hours ago, eric240sx said:

When having new piston rings, do you need to keep the engine in high RPM or low?

You want moderate RPM (3-5k) and high cylinder pressure (ie full throttle).  Combustion pressure pushes the rings against the cylinder walls.

Warm up the engine to full operating temperature by gentle driving first.  Then do full throttle from 3k to 5k RPM.  Drive gently for a while then do it again.  Repeat a few times giving the engine light throttle in between.

You really only have about 50-100km after a fresh rebuild do this, after which it makes very little difference.

Of course if your engine builder gives different instructions you'd be wise to follow it, they may know more than me
 

[eric240sx]

9 hours ago, Kinks said:

You want moderate RPM (3-5k) and high cylinder pressure (ie full throttle).  Combustion pressure pushes the rings against the cylinder walls.

Warm up the engine to full operating temperature by gentle driving first.  Then do full throttle from 3k to 5k RPM.  Drive gently for a while then do it again.  Repeat a few times giving the engine light throttle in between.

You really only have about 50-100km after a fresh rebuild do this, after which it makes very little difference.

Of course if your engine builder gives different instructions you'd be wise to follow it, they may know more than me
 

I would really love to follow your instructions but I haven't tuned my car after installing a bigger turbo so I can't quite go full throttle ?

 

I can idle the car, of course, Im going to redo a compression test and then do the wet test and see if I gain any psi 

[Trex]

Through my years I've found everyone breaks in engines differently.
I have some mates who gently ease into boost and power, and some who flog the absolute hell out of them straight from first start.
Again there are a lot of variables with different engines and parts used

[KiwiRS4T]

If you don't run it hard from the off you can glaze the bores and it will always use oil. If you are pulling the head off you need to get a cross hatch happening on the cylinder walls with a suitable hone.

But the two spark plugs on the left indicate a more immediate problem. Why are they rusted? Where is the water coming from? Is it leaking from the head or just some over-enthusiastic hosing of the engine?

Your compressions are way too low. Test is ideally done with a hot engine. All plugs removed. Pull lead off the CAS. Test 1- 6 and then as above drop some oil in each cylinder and repeat.

You shouldn't be racing it untuned. Do you actually have an aftermarket ECU? Have you just dropped in bigger injectors without tuning for them? You may just have washed away the oil from your rings with excess petrol.

[eric240sx]

1 hour ago, KiwiRS4T said:

If you don't run it hard from the off you can glaze the bores and it will always use oil. If you are pulling the head off you need to get a cross hatch happening on the cylinder walls with a suitable hone.

But the two spark plugs on the left indicate a more immediate problem. Why are they rusted? Where is the water coming from? Is it leaking from the head or just some over-enthusiastic hosing of the engine?

Your compressions are way too low. Test is ideally done with a hot engine. All plugs removed. Pull lead off the CAS. Test 1- 6 and then as above drop some oil in each cylinder and repeat.

You shouldn't be racing it untuned. Do you actually have an aftermarket ECU? Have you just dropped in bigger injectors without tuning for them? You may just have washed away the oil from your rings with excess petrol.

Very insightful thoughts, when I did my full rebuilt, it was on stock engine and ecu and that's when I raced it. But then the stock setup started burning oil and I foolishly though it was turbo seals and 5k after the upgraded parts, the car is still burning oil. 

I performed a compression test yesterday, every cylinder had around a 45% compression increase when oil was dropped in there 

 

Dry test 

cylinder 1: 55

cylinder 2: 60

cylinder 3: 70

cylinder 4: 70

cylinder 5: 65

cylinder 6: 70

 

Wet test 

cylinder 1: 115

cylinder 2: 135

cylinder 3: 130

cylinder 4: 115

cylinder 5: 120

cylinder 6: 120

Note that the engine has a thicker 1.5 cosworth headgasket 

[Birds]

That dry test is pretty low^

Tried dropping the oil to take a look? Could / would be full of petrol smell it the rings aren't forming enough of a seal

[eric240sx]

4 hours ago, Birds said:

That dry test is pretty low^

Tried dropping the oil to take a look? Could / would be full of petrol smell it the rings aren't forming enough of a seal

I feel like the piston rings or cylinder wall are bad 

[eric240sx]

I've done some research and I just realized that it is unlikely for all 6 cylinder walls to be messed up all at once, but the piston rings go out together so it has to be the rings. Unless the rings were so bad it damaged the cylinder walls

 

"if you liked it then you shoulda but a ring on it " - Beyoncé 

 

[89CAL]

Why don't you pull the head and find out instead of getting people to guess in an online forum

Compression. Results that low mean something is def wrong so I wouldnt bother searching for a reason to pull the head beyond that