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Oil consumption and compression test

Mike R

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Hello all,

Hope you can help with this one - I'm pretty confident with most bits on the GT6, but don't have much experience once you get into how to fix the engine itself.

Going to/from LeMans I found that my oil consumption was higher than expected - around a litre over 600 miles.


Investigation done:

* external oil leaks - slight weep from head gasket spark plug side about half way along head, but not enough even to drip onto floor of garrage just gives the block that "wet look". Looks damp around dipstick tube, but could be just it collecting there from same source. Nothing else obvious. Don't think that would be cause of the quantities i'm looking for - that would be a regular drip.


* engine blow by test - put a latex glove over crankcase breather, inflates in about 10secs when at idle. From what i can find that seems quite a low blow by.


* rev engine whilst watching exhaust - no smoke, blue or otherwise.


* dry compression test:

All cylinders apart from no.2 at 130 to 140 psi. No. 2 cylinder at 90psi.


* wet compression test:

No. 2 cylinder now at 110psi, 20 psi increase over dry.

No. 6 cylinder now at 145psi, 15 psi increase over dry.


* cylinder leak down test:

This uses compressed air to measure leak rate when cylinder at TDC. All cylinders apart from no. 2 at 25 to 30% and right in middle of green section on the gauge.

No.2 cylinder 45% and in the amber section of gauge. A bit of oil in the cylinder and it improves to 40%.

Glove placed over exhaust - no inflation - hence exhaust valves fine?

Radiator cap remove a little water added so top hose entry submerged - no bubbles - so head gasket fine?


My conclusions.

I think the increase when putting oil in the cylinder is small and similar to the increase seen on the good cylinder with oil. I think this shows that the problem isn't the rings?

I think the exhaust valve, and head gasket are fine, so that just leaves the inlet valve.

I'm thinking a worn valve guide has let oil down the valve causing deposits on the back of the valve head and making it not seat?


Right .... So now the questions .......


1. Do you agree with my assessment from the investigation? Or have I missed something?

2. Is it possible to re- seat a valve by lapping in again? Will this deatroy the lead memory?

3. Is 15 to 20 psi increase between dry and wet compression tests normal? Or is an indication that all cylinders actually need work?

4. Any experience of fitting valve stem seals - do they work? Any risks?

5. I was thinking of replacing all 6 inlet valve guides, fitting valve stem oil seals on them, lapping in no. 2 valve. Is that a reasonable DIY job?

6. Anything else?


Sorry for war and piece on this ... but hopefully it make an interesting read if nothing else!




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do you have an awful external oil feed to the rockers,  is so take it off, 

as std there's not a lot of oil volume in the rocker box , i doubt this is your cause for consumption,, you can fit guides with care and a suitable drift they do  move , even make a threaded stud to use as a drag,

seals not normally needed as there's not much  oil to seal out.

lead memory i have reground valves with paste and they lasted many thousands of miles, if you have the seats recut and the valves ground then you probably will loose memory. if they are that bad then its a good time to fit exhaust seats.


some will say 600 per litre is within  triumph spec ,   but large oil useage is normally a  unseen leak underside , or rings worn out 

interesting series of tests .  were the plugs all out and throttles open ??


just some ramblings   Pete

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Comprehensive diagnosis! Agree with Pete. Your initial problem was oil loss and you've found a problem with number 2 cylinder, yes it's low. However you don't appear to be burning oil so the problems may not be related.


The wisdom these days is don't un-lead the head till it needs it. So if you really want to, regrind the valve, at least then you'll know a bit more.


It leaks oil, that's how you can tell it's a Triumph!

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Thanks Doug & Pete,

Pete - no I dont have the evil that is the external oil feed. But for my sins I did install it when I first owned the car in 2000. I then read the problems and removed it within 6 months.

Yes plugs were out and throttle open (accellerator chocked with a piece of wood)


I don't suppose either of you know if the 15psi difference between wet and dry compression tests is normal do you?


You both seem to be saying 600 miles for a litre of oil isn't that bad - is that right?


If so, I might just live with it, because otherwise she's performing really well.


What's your thoughts?



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I like your diagnostic skills, Sir!

Especially the rubber glove test - that needs quantifying, as it's very subjective, but a brilliant idea!


1/ Your Interpretation seems to implicate a leaking valve on No.2, which I don't agree with.   A significant increase in Compression after oiling means a ring seal failure, not a valve.

2/ Lapping a valve WILL lose 'lead memory', but then the fears of recession are largely unfounded, unless you stress it by high revs for long periods - motorway or Le Mans driving , but that's only every two years!

3/ I think that 15psi when 'wet'  is at the upper limit of normal, so all your rings may be getting tired.

4/ Valve stem seals, No experience, lots have, few have reported results.

5/ No, or I doubt you have the kit, I don't.   Valve guides need to be pressed in or out, and a sufficiently powerful press is unlikely outside a machine shop.  Then, they need reaming back to size, as they will have been squeezed in that process.

6/ 1, 2, 3, despite your rubber glove test, tell me that rings are your problem.    But that oil usage, and the pressure down on No.2 are not serious.    Monitor for now,



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It all depends on yer oil too,

olde oil will revert to a low grade so be thinner than new oil

And, been giving it some stick, high revs, oil will be alott lott thinner, so use moer.


IE, a 20 /50 will be thin wen hot, thicker wen hot,{supposedly }

butt, if its olde, its broken doon, { lots of cheeper oils doo this }

then it,ll be staying at a 20Weight, thus going past rings /guides.


Change oil, get a good oil,like Penrite 20/60,

Also, if yer breather valve is blocked, then it,ll mek pressure int engine, an force oil past rings,oot of seals.


try above, then see wots wot with oil usage


if it aint a new oil, or breather  cure,    then its a worn piston ring  thingy


Can,{ butt its most likely too late noo }  go to a long incline, or use yer brakes, and use full throttle at 2-3000 rpms in top gear for as long as ye can hold it,

and try this a good few times

it will get some pressure beint the rings, maybe just enought to bed em,or blow oot any carbon build up in there

worth a try, but likely too late noo.


re diff pressureon cyl test, , this really aint a bigg thing     IF,  its repeatable after a few hundred miles

reason, rings , contrary to pop belief, doo move aboot in the grooves

some time for the better, some times for the wuss

yours maybe at a bad point




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Some more good replies ... Much appreciated.

John ... The thing about no.2 cylinder is .. Is the increase when "wet" significant. I assumed it wasn't because i had a similar increase on a good cylinder, hence the question what is normal. And my crank case blow by test seems to support that its not rings. But if you're telling me I shouldn't be seeing that sort of difference on any cylinder, then looks like I've got some work to come!


And, yes car working very well at mo .... If it wasn't for the oil consumption I wouldn't have a problem at all.


GT6M - thanks for the tips - i use a 20w 50 thinks its Duckhams, but a reasonable brand with API marking etc.

I dont have a breather valve, it breaths via a knock out pot to atmosphere, there's no back pressure which is apparent by opening the oil filler. Guess the tip on bedding in is more for a newly rebuilt engine? Or might it help an old one like mine?


Anyway ... For now I'll keep monitoring, but at some point I'll need to decide on what works needs doing, recon cylinder head or complete engine? It hurts just to type it!



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Comprehensive diagnostic process.


It's an engine with some wear.  But the 2L six dies slowly and it'll keep soldiering on.  A head overhaul will probably help even up your compressions but I don't think it'll have any effect on the oil consumption.  Without an external rocker feed there's not alot of oil going to the top end.  In the absence of any significant oil leaks most of the oil loss is via the rings and being burnt.  


As already noted, the type of oil used will affect the consumption and not all 20/50s are equal in this.  You can take the expensive oil route or stick with a mid-range one and add a can of Wynns which I have found to be very effective at reducing oil consumption.  My Vitesse engine survived on the stuff for about 5 years with it improving the oil use from 1L/300 miles to 1L/ 1000 miles+ and that included some fairly testing treatment over long distances.  Yes, it's a bodge, but alot cheaper than a rebuild if the engine is otherwise running well.



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try a running test, will pin point either valves or rings much much better.


read thru eer,  ot google running test.

Ive always used it


Running Compression Tests - ALLDATA Support





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Thanks Nick and GT6M -

I'd never heard of the running compression test. That looks interesting, I might give that a go.

As I don't have any performance issues / symptoms I'll definitely try a different oil. Hopefully that will give me a few more years to save a few pennies for a posh rebuilt engine. Or maybe try the rebuild myself, although not sure I'm brave enough for that.



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Very good test




dry test shows number two cylinder at fault .

Using oil into cylinder proves that the compression rings have worn allowing gases to escape but oil rings is ok -  ( hence no smoke)

with the compression reading still not getting to the same level as the other cylinders you could still have an inlet valve problem. Re-lapping the valves should cure this.


If you are intending to remove head

turn the head upside down and pour petrol into the recess of the head covering the valve heads. Once valves are covered

Go for a coffee - on return and the petrol is now on the floor you found the problem .


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  • 10 months later...

Sorry for opening this one up again but it's a simple question


Using a good quality 20W50 oil and with no particular oil leaks. what miles per litre would be needed to start thinking about looking at getting work done to resolve?





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Hi Pete I have the correct min level when I added a further litre to find the max it went well over the original max level After covering 1500 miles in France it was pretty much back down to the min level That's still within the tolerances Dave has kindly stated so I am not going to worry The oil pressure has been good all the way to


Thanks for the info both



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