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Fuel/Oil Contamination


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Hello All, 

Every year or there abouts I have an engine oil sample sent off for analysis, why? Because I'm funny like that. I use Millers service for this. A sample taken at the end of last year showed 4% fuel dilution, quite a lot me thinks. I put this down to me maybe taking the sample after warming the engine up only idling in the garage. So, fresh oil & filter fitted, almost another 1,000 miles covered and a sample taken last week immediately after a 120 mile trip, sample retrieved via the dipstick tube with the engine running.

Lab results show 3.5% fuel dilution???

Car runs superbly, no smoke, injectors spray pattern perfect, fuel pressure circa 110psi at the M/U, no fuel present at the tell tail hole in the dizzy/MU pedestal, besides if fuel were to enter the engine via the pedestal it would have to get past two lip seals, quite impossible.

This one has me stumped, anyone have any ideas on this?

Richard.

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Would be interesting to know what Millers suggest would be a reasonable acceptable figure for the age of the engine, it may be just a reasonable figure and nothing to worry about perhaps?

John

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Thanks John,

The engine has only done around 5,000 miles since rebuild, I've been sampling the oil for the past 2-3 years, the fuel dilution is something new. However, if there are any other forum users running a Pi and have the oil sampled, it would be interesting to hear what results they get.

Richard.

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Is this a correct assumption or am I remebering this wrongly?

There is a tell tale drip hole between the two lip seals?

I  imagine you would get a drip of fuel (or oil) from the weep hole between the two back to back lip seals in the MU to distributor housing if there were a seal failure. 

1672226897_MUpedestaldrain.jpg.20a723247d1c7f17946ccee00fef552b.jpg

Peter W

PS Acknowledgement - Image from Rimmers Web Page

PPS  Try cleaning the drip hole out in case it is blocked and see if fuel (or oil) comes out.

Edited by BlueTR3A-5EKT
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Thanks Peter,

Tell Tale hole is clear, checked that last week, besides, as said, both seals (viton) would have to fail to allow any fuel to enter the engine.

Richard.

P.S. Assumption is correct, there is a tell tale hole.

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I can only think of two paths for fuel to get into the oil:

1) Leaking past the seals in dizzy/MU pedestal. It can leak past the two seals, though it should be evident at the tell tale hole. Is the hole clear?

2) Unburnt fuel in the upper cylinder getting past the rings. Maybe an injector dribbling fuel after stopping engine?

It would be interesting to know if a degree if dilution is normal, I don’t suppose many people get their oil analysed.

Mike.

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12 minutes ago, michaelfinnis said:

I can only think of two paths for fuel to get into the oil:

It would be interesting to know if a degree if dilution is normal, I don’t suppose many people get their oil analysed.

Mike.

Yes Mike, I'm hoping that another Pi user is as deranged as I am :huh: and can share their results.

Richard.

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17 hours ago, Richard71 said:

Thanks John,

The engine has only done around 5,000 miles since rebuild, I've been sampling the oil for the past 2-3 years, the fuel dilution is something new. However, if there are any other forum users running a Pi and have the oil sampled, it would be interesting to hear what results they get.

Richard.

Hi Richard!

When you say the engine was rebuilt 5000miles ago, was it re-bored? Or just bores honed and new rings fitted? I have always understood that there is fuel contamination in the oil but as already said above what is the acceptable level? That is some thing I do not know? It is definitely a question for Millers.

Bruce.

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28 minutes ago, astontr6 said:

Hi Richard!

When you say the engine was rebuilt 5000miles ago, was it re-bored? Or just bores honed and new rings fitted? I have always understood that there is fuel contamination in the oil but as already said above what is the acceptable level? That is some thing I do not know? It is definitely a question for Millers.

Bruce.

Thanks Bruce,

The engine was indeed rebored, new pistons & rings etc. According to the sample records it started out 0%, 1%, 1.2%, and so on until 4% in oil with 1,000 miles use. I doubt the problem lies with the Pi system itself, injectors are giving a good spray pattern, but having said that, perhaps now the engine is well broken in, maybe there is a permissable amount of fuel passes the rings?

Like I said above, it would be good to know if another Pi user samples their oil and would share the results.

Richard.

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1 hour ago, Richard71 said:

Thanks Bruce,

The engine was indeed rebored, new pistons & rings etc. According to the sample records it started out 0%, 1%, 1.2%, and so on until 4% in oil with 1,000 miles use. I doubt the problem lies with the Pi system itself, injectors are giving a good spray pattern, but having said that, perhaps now the engine is well broken in, maybe there is a permissable amount of fuel passes the rings?

Like I said above, it would be good to know if another Pi user samples their oil and would share the results.

Richard.

Is there any black smoke coming out of the exhaust when you boot it? What colour are the spark plugs? After my engine was re-built my m/u went all rich and I had to get a new part ex from KMI.

Bruce.

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Here’s a thought.  

Glazed bores.  

Needs an Italian tune up.  
I think the trick is…..Full throttle up a hill with engine doing 2.5-3 k RPM. 
 

Peter W

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2 hours ago, BlueTR3A-5EKT said:

Here’s a thought.  

Glazed bores.  

Needs an Italian tune up.  
I think the trick is…..Full throttle up a hill with engine doing 2.5-3 k RPM. 
 

Peter W

That's good advice from Peter. Just needs for the gearbox to be in 4th gear, it relies upon the engine expanding the piston rings and bedding them into the glazed bores (having the cylinder bores washed with petrol helps cause this). Google Brake Mean Effective Pressure (BMEP) it's a known fix.

Mick Richards

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 3.5 and 4 % are close and suggest to me that along drive does not increase contamination. which argues against blow-by. Perhaps contamination depends upon th number of cold=starts , use of fuel-enrichment ( the choke) and "bore-wash". 

Peter

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4 hours ago, Peter Cobbold said:

 3.5 and 4 % are close and suggest to me that along drive does not increase contamination. which argues against blow-by. Perhaps contamination depends upon th number of cold=starts , use of fuel-enrichment ( the choke) and "bore-wash". 

Peter

Possibly too many cold starts then left idling for long periods?

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