Leak down test - confused about the results

[dom14]

I just did the leak down test for my Nissan Patrol GQ RB30.

The test results came out ok for all the cylinders.(The leakage is closer to 0%)

Then I removed the SCHRADER VALVE and gave around 90-100PSI directly to the cylinder(s).
To my surprise, I heard hissing noise coming out of the oil cap on the rocker cover.
It happens for all the cylinders in equal strength.
Also the leakage reading without the schrader valve is around 20-25 % for all the cylinders.

I'm having trouble decoding this information guys.

Can I have some assistance with that, please guys?!!

Here's the leakage video.

https://www.youtube.com/watch?v=vftd7uS2vm8&feature=youtu.be


1)Why is the leak down test leakage is higher without the schrader valve?
Because it's leaking from the oil cap I guess(Meaning leaking from the piston oil rings or something??!!)

2)Is the amount of leakage(hissing) is acceptable for this car???!!
>>>no leakage with schrader valve, 300k+ on the odometer, head and gasket done just before 300k, it's
325k now<<<<


I had to get the cylinder at TDC on compression stroke before I attached the spark plug socket adapter. So, I'm not sure how the 90-100PSI pressurized air from the compressor get into the cylinder bore with the schrader valve!!!

3)Schrader valve should stop the compressed air getting into the bore, wouldn't it(it's one way valve)???!!

And the air inside the bore is not compressed to 180PSI(the typical cylinder TDC pressure), because I had the spark plug hole opened to find the TDC(ballon & screw driver trick). So, when I attached the spark plug adapter(with schrader valve in), the pressure inside the bore is still 1PSI(normal atmospheric pressure), not 170-180PSI.
If you guys look at the picture(s) with the schrader valve, what shows in the picture is the spark plug socket end of the adapter with the schrader valve.

4)So, the pressurized air from the compressor can't get into the cylinder bore??!! Right??!!

5)So, without any pressurized air inside the cylinder bore, how would I(or the leak down tester gauge) know whether the cylinder has leakage or not??!!!

I'm a bit confused at the moment guys. Need some expert tips to get my head cleared about this.
Thanks in advance.

[4bye4]

Hi mate. You have got me confused as well and I use leakdown testers all the time. First my LDT does not have a schrader valve. you simply set the gauge at full scale then plug the test lead which is screwed into the spark plug hole, or if it is a diesel, into a glow plug hole, into the guage.

Don't complicate things by trying to read PSI drops etc. If the guage is in the green its OK. If its in the green but near the yellow, the cylinder is worn and leaking. Thats when you start to listen and try and hear where the air is coming from. From the dipstick hole, probably rings. From the exhaust pipe, probably exhaust valve. From the carbi or inlet manifold, probably inlet valve..
So to answer your questions.

1)Why is the leak down test leakage is higher without the schrader valve? Because with the shrader valve in it, it is measuring the shrader valve not the cylinder

2)Is the amount of leakage(hissing) is acceptable for this car???!! Probably, its not real bad being in the green and not even half way through that. You will always get some hissing through valve stema and rings. This is because the leakdown test is holding pressure for a long time where as when operating the cylinder only has to hold pressure for milliseconds. The cylinder is not airtight. It is just a chamber which directs the expanding gasses onto the point of least resistance ie. the piston.

3)Schrader valve should stop the compressed air getting into the bore, wouldn't it(it's one way valve)???!! I agree. As I said my tester does not have a shrader valve. A shrader valve would be more useful in a compression tester.

4)So, the pressurized air from the compressor can't get into the cylinder bore??!! Right??!! Agree. As above.

5)So, without any pressurized air inside the cylinder bore, how would I(or the leak down tester gauge) know whether the cylinder has leakage or not??!!! Agree. As above.

From what I am reading I would think the test is OK. Is there any difference between cylinders?

[dom14]

Hi mate. You have got me confused as well and I use leakdown testers all the time. First my LDT does not have a schrader valve. you simply set the gauge at full scale then plug the test lead which is screwed into the spark plug hole, or if it is a diesel, into a glow plug hole, into the guage.

Don't complicate things by trying to read PSI drops etc. If the guage is in the green its OK. If its in the green but near the yellow, the cylinder is worn and leaking. Thats when you start to listen and try and hear where the air is coming from. From the dipstick hole, probably rings. From the exhaust pipe, probably exhaust valve. From the carbi or inlet manifold, probably inlet valve..
So to answer your questions.

1)Why is the leak down test leakage is higher without the schrader valve? Because with the shrader valve in it, it is measuring the shrader valve not the cylinder

2)Is the amount of leakage(hissing) is acceptable for this car???!! Probably, its not real bad being in the green and not even half way through that. You will always get some hissing through valve stema and rings. This is because the leakdown test is holding pressure for a long time where as when operating the cylinder only has to hold pressure for milliseconds. The cylinder is not airtight. It is just a chamber which directs the expanding gasses onto the point of least resistance ie. the piston.

3)Schrader valve should stop the compressed air getting into the bore, wouldn't it(it's one way valve)???!! I agree. As I said my tester does not have a shrader valve. A shrader valve would be more useful in a compression tester.

4)So, the pressurized air from the compressor can't get into the cylinder bore??!! Right??!! Agree. As above.

5)So, without any pressurized air inside the cylinder bore, how would I(or the leak down tester gauge) know whether the cylinder has leakage or not??!!! Agree. As above.

From what I am reading I would think the test is OK. Is there any difference between cylinders?

Hi mate,

Thanks for the super fast reply. I understand now. It couldn't be clearer now.
The leak down tester came with the adapter which had a schrader valve in it already, which it shouldn't have or they might have expected me to remove it before I use it. I know these testers are meant for pro mechanics who know what they're doing.
So, it's obvious all my first round of test on each cylinders which came out leak down as zero was incorrect.
I didn't do all the cylinders without the schrader valve. I think I missed that in couple of cylinders, so I'm going to have to do it again.
Last time when the head gasket was gone cactus, it was the cylinder three & four that was filling up with water.
So, I expected those cylinders to have more leakage, but it didn't look that bad, close to 25% but still in the green area.
But, I have to do the test without schrader valve for the all cylinders again, to be 100% sure.
I will post the results later today.

I have or I might have created another unexpected problem.
I might have dropped the schrader valve into the 6th cylinder.(Yeah, clumsy and stupid me, I forgot to screw in the schrader valve, when I was fiddling with it for the photos above). The cylinder is still on compression TDC.
I blew some pressurized air into it to see/hear if I can hear some rattling of the dropped schrader valve in there, but I couldn't hear anything.
Then I used a vaccum cleaner and blocked the air as much as I could and ran it. That didn't suck any schrader valve out of the bore.
So, I reckon I may have dropped the schrader valve into the engine bay, but not into bore, but I'm still concerned about this.

In case, the schrader valve is still inside the bore and stuck in the upper wall,

Can I leave it there and hope it will get blown out of exhaust valve and hopefully out of the exhaust???!!

Thanks again mate.

Dom

[4bye4]

Mate, in a nutshell, if you have dropped somthing into the cylinder DON'T TURN THE MOTOR OVER. It won't come out the exhaust it will get stuck in a valve, resulting in no compression - pull down, or it will get jammed between the piston and the head - pull down, or it will shatter and give you a cylinder hone which you don't want - pull down or evn cylinder liner - BIG $$$. Either find the lost bit or take the head off! Sorry.
You mite try a magnet on a stick down the spark plug hole BUT DON'T DROP IT IN THERE!

[dom14]

Mate, in a nutshell, if you have dropped somthing into the cylinder DON'T TURN THE MOTOR OVER. It won't come out the exhaust it will get stuck in a valve, resulting in no compression - pull down, or it will get jammed between the piston and the head - pull down, or it will shatter and give you a cylinder hone which you don't want - pull down or evn cylinder liner - BIG $$$. Either find the lost bit or take the head off! Sorry.
You mite try a magnet on a stick down the spark plug hole BUT DON'T DROP IT IN THERE!

I had to turn the motor today mate. I didn't have a choice. I had to do the leak down test again.
I don't think the schrader valve is in the bore. I will try the vacuum cleaner trick again tomorrow.
I got worried, because I couldn't find the schrader valve anywhere near. But, if it was dropped inside the engine bay, it's pretty much impossible to find. So, that may be the case.
I would like to think that there has to be a way to get it out, if I drop something inside the bore through the plug hole.

You don't think the vacuum cleaner method can work??!!

Telescopic magnet I got is too thick to get through the plug hole. I will grind the sides of it and try it tomorrow.

Here are the readings again. This time, I took my time and did it properly. No schrader valve involved, except the possibility of a schrader valve stuck inside the cylinder 5. :)

BTW, cylinder 5 reading is actually around 15-20%. The coupling between tester and the adapter hose started leaking, I had to hold it by both hands to get the correct reading, but couldn't take the photo while holding it.

[dom14]

I guess, I can use one of those flexible telescopic inspection camera thing to see inside the bore. That if I can find a one cheaply.

[4bye4]

Dom, those readings look reasonable. Why are you testing. What are you looking for. Is the motor missing or low on power or what. LDT is an diagnostic tool as is compression test to try and determine why something is happening. What is happening that made you go down this Leak Down Test path.
I agree that the schrader valve is probably not in your cylinder. You would have to be pretty unlucky to drop it in through the spark plug hole.
Tony

[dom14]

Hey Tony,
Yes, I've been doing the LDT to rule out possible issues with the rings, valves, valve guide seals, etc.
The reason was because of few issues that we've discussed in a previous thread.

http://www.nissanpatrol.com.au/forums/showthread.php?30489-Compression-test-amp-Leak-down-test

Basically,
1)Smokey during idling, when the engine is cold or warm
2)Started hesitating, stalling, cutting out and then refuse to start on LPG, which spread to petrol as well
3)Now, the car sometime even fail to start on petrol as well and stalls and cuts out after few minutes of running, even on petrol.
4)Blows oil out of rocker cover, regardless of gasket(s) are in good condition and properly sealed(PCV is fine)
5)There's a small leak of brake oil that I can't locate(need topping up once a month or so)
6)Couldn't start on LPG, even after installing a new cold start solenoid professionally.
7)Fair bit of carbon build up on spark plugs from last two weeks or so.
8)It was burning oil and the old oil looked pretty bad.

All these points out to an ignition issue, carby issue or a brake vacuum system issue which I'm still working on.
I wanted to ascertain there are no issues with the engine mechanics, before I get deeper into above three areas.
That because the above symptoms can be produced by a badly worn out engine, faulty or worn out valves, etc.

So, tomorrow is going to be a busy day for me. :icon_bonk:
If you have any more helping tips for me, I'm happy to absorb any many.

Cheers .;)

Dom

[4bye4]

Hi Dom,
Wow you have certainly got a lot of things to choose from. OK just to set the record straight, I am a small motor mechanic/engineer not an automotive mechanic. I have built a few race motors though and have a good idea of motors in general.
Ok having said that, I have and still do use leak down testing a lot, and IMO the readings that you are getting are not to bad. I am intrigued by the brake fluid usage. This is pretty wild, but is it possible that you have a leak in the vacuum assist for the breaks and are drawing break fluid into the inlet manifold. Many years ago I had an excessively smoking Ford Telstar which turned out to have a hole in the automatic transmission kick down diaphragm. Only way I picked it was that it was burning oil but not using oil. It was burning transmission fluid.
Anyway if you were somehow pulling brake fluid into the inlet manifold, that would explain the smoke and pretty much all the points except maybe 4 and 8. The oil from the rocker cover intrigues me because if you are getting pressure in the rocker cover why is it not being taken care of via the PCV system, and where is it coming from. Normally excessive oil in the rocker cover is blowing back from the sump or coming from the valve stem seals, but valve stem seals usually only cause the motor to smoke at start up. Might have to hope other forum members are following this and can get involved. I can't help thinking that I and maybe you as well are missing something simple and over complicating the issue.
Tony
:confused:

[dom14]

Hi Tony,

Yes, I get your point. It's quite possible I may be missing something simple and over complicating the issue.
But, I reckon that's the 'easy' way to learn if I'm to learn to fix things in this car by myself.:1087:
I'm pretty sure brake oil isn't 'leaking' per say, but rather getting burnt somewhere as well. But to be 100% sure, I'll do another thorough check in & around
the car to see any leaks. It's a slow leak, so it's still possible I can miss it(I'm a four eyed one :tongue:)

I do feel there's an issue with the brake booster vacuum system. Since this is a new area for me, I'm going slowly at it.
Is it possible that brake oil can get sucked into the carby and damage the seals and vacuum lines?

I'll keep posted of the outcome of my tests today.

Cheers

[4bye4]

Hi Dom,
Had a chat with a mate last night :gossip: (he is a mechanic) and his verdict is that the oil rings have gone. Possibly the motor has overheated and cracked one or more oil rings. The compression and LDT will not show this if the compression rings are OK. We wonder why #6 is reading better than the other cylinders. If we are correct in our assumption that the motor has overheated due to excessive lean mixture, number 6 cylinder would be the most affected. Looking back over your test results, number 6 is different in LDT and no5 and no6 are low in compression test. looking back through all your posts on this, that is the conclusion we have come to. Looks like a pull down. Tony :frown:

[dom14]

Hi Tony,

That doesn't sound too good. :(
I knew I need to rebuild the bottom end sometime soon, but I wasn't expecting it to be this time.
I thought I can put it off until the EFI conversion project and the possible turbo project, for next year.

Only thing that puzzles me is that I usually keep an eye on the temperature gauge and has never noticed an overheat, other than the gasket blowup two years ago.

1)How did the excessive lean mixture happened??!!
2)Is the oil blowing out of rocker cover consistent with the oil ring damage/wear?!

BTW, no 5 & 6 both have the same LDT reading, which is 15%. What'showing on No 5 photo isn't correct(the adapter hose leakage issue).
Other four are obviously showing a higher LDT reading.

BTW, the oil blowing issue(out of rocker cover gasket) isn't that heavy(but annoying enough). It takes few weeks of driving to see it.
I've seen some fellas using a catch can to collect the oil, but I reckon that's for turbo converted engines of this Nissan RB30.
From time to time, I can even smell the oil while driving, which tend to change from season to season.

Thanks
Dom

[dom14]

No 5 & 6 compression readings(170PSI) are lower than the rest, and no 5 & 6 LDT readings(15%) are also lower(better) than the rest

[4bye4]

Hi Dom,
Just thought I'd check if any further advanced. I was hoping some other members may weigh in on this one. I haven't given up on you, just run out of ideas at the moment.
Tony

[dom14]

Hi Dom,
Just thought I'd check if any further advanced. I was hoping some other members may weigh in on this one. I haven't given up on you, just run out of ideas at the moment.
Tony

Hi Tony,
I pulled the carby out. It was last year I rebuilt it with a kit, but I managed two monumental mistakes.

1)I didn't use carby cleaner to clean it, but used petrol instead & I didn't blow every single hole in it with compressed air(only some of them)

2)I used silicon sealant(in addition to the new gaskets) for the carby compartments.( I could see the silicon pieces oozing out of the edges into the carby interior through the top hole)

Last year I did the carby job, because of an idling problem(motor stopped idling altogether) My rebuild job fixed the problem. Also I had some help from a forum guru here, who came over to my place and gave me some great tips on how to do it. He was a mechanic. I fixed the problem, but my inexperience and impatience caused me to do a too quick of a half job.

This time I'm getting a similar problem. Starting issues as well as idling issues.

I'm not sure whether I should get it professionally rebuilt, but I'll give it a good clean and remove all the silicon grime and then use a fresh gaskets.
Then I would have to do my best adjust the idle mixture screw and idle speed screw.
Last time I put a screwdriver inside the bonnet and drove around the town, fiddling with the screws, until I got the right setting, though it didn't last that long.
It's a heck of a job to tune a carby for both petrol and LPG. Then having to redo it over and over with crazy Melbourne weather changing from winter to summer within a half day.:bananarock:.

I'll see how it goes tomorrow. Advice given to me by the forum buddies was to pinch an EFI dongle kit from a VL and put into this RB30.
Only reason I haven't done it yet it because, it was going ok so far with the carby up until couple of weeks ago and fuel economy was great too.

I will have to start hunting for a VL commodore EFI kit, as well as a low km motor for that project.

I"ll keep you posted with the outcome of the carby repair job tomorrow.
I better get the troll going by the end of tomorrow, because I need fella for the weekend. :biggrin:

Cheers
Dom