Oil Analysis: Fuel Dilution
Orig. Posting Date | User Name | Edit Date |
Jan 19, 2019 11:50AM | Rosebud | |
Jan 19, 2019 10:57AM | h_lankford | |
Jan 19, 2019 10:32AM | Rosebud | |
Jan 19, 2019 10:01AM | Rosebud | |
Jan 18, 2019 04:40PM | 1963SV2 | |
Jan 18, 2019 02:42PM | Rosebud | |
Jan 18, 2019 01:37PM | malsal | |
Jan 18, 2019 12:50PM | Rosebud | |
Jan 4, 2019 02:23PM | Rosebud | Edited: Jan 4, 2019 02:27PM |
Dec 22, 2018 08:29AM | Dan Moffet | |
Dec 21, 2018 09:22PM | Rosebud | |
Dec 21, 2018 08:18PM | h_lankford | |
Dec 21, 2018 06:08PM | Rosebud |
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I replace the connectors and will try starting 'Rosebud' again this morning. Will advise.
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Re: Fuel pressure. A couple of weeks ago I began switching off the fuel pump 30 seconds before shutting the engine down to avoid static pressure in the fuel line bleeding into the carbs. Some thought that was the source of the gas in my oil sump. Turns out 30 seconds is way too long; caused a fuel starvation sputter after a minute or two of driving. That's what led me to think the cut-out problem was related to low fuel pressure. I'm now switching off the pump 5-10 seconds before shut down. The next oil analysis will determine if I've solved the gas-in-the-oil problem.
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The original Smiths tachos were prone to interference in the trigger line. Mine always wandered a bit until a mate made me a filter which was placed in the line just before the tacho to clean up the signal.
Cheers, Ian
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The original Smiths tachos were prone to interference in the trigger line. Mine always wandered a bit until a mate made me a filter which was placed in the line just before the tacho to clean up the signal.
Cheers, Ian
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It's always something…
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If in doubt, flat out. Colin Mc Rae MBE 1968-2007.
Give a car more power and it goes faster on the straights,
make a car lighter and it's faster everywhere. Colin Chapman.
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So, as an added measure I've been switching the fuel pump off about 30 seconds before shutting the engine down which brings the residual line pressure to zero. I'll put a couple thousand miles on the oil and send another sample in for testing. Will post the results here. Thanks all.
It's always something, eh?
.
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Fuel pressure is now at 2.5 psi and remains so for up to an hour after shutdown which is still a concern. So, as an added measure I've been switching the fuel pump off about 30 seconds before shutting the engine down which brings the residual line pressure to zero. I'll put a couple thousand miles on the oil and send another sample in for testing. Will post the results here. Thanks all.
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In a SU carb, the proper fuel level is very close to the top of the carb jet. If too high in the bowl, then it is too high in the jet for proper air/fuel mixture. If the bowl is over-filled, then the level would be higher than the tip of the jet and the carb bridge. At that point it trickles out.
If your bowl float jet/needle is worn or sticky, there is the potential for it to stick open. The top of the fuel tank is higher than the carb. If your tank is full, and you float jet is stuck open, gravity will let the tank drain until the fuel level in the tank is the same as the top of the carb jet. My Mini proved that one winter. I used to winter store the car with a full tank to minimize condensation. The carb float jet stuck open and 2 - 3 litres of fuel drained into my crankcase. Luckily I checked the oil before starting the engine in the spring. Now I leave it with no m ore than half a tank.
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"Hang on a minute lads....I've got a great idea."
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…Also, boron is as on the high side. Anyone know if boron is used in any critical engine/transmission parts? I use a carbon inhibitor fluid every couple of tank fulls—I'll check the label to see if boron is an additive.
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I got the results of my oil analysis the other day and everything looks good except that it shows an excessive amount of fuel in the oil. The testing lab suggests the high gasoline content is a result of 1) piston ring blow-by 2) frequent short trips 3) excessive idling 4) timing/mixture issues. I normally change my synthetic oil @ 3K miles—I stretched it to 5K this time in anticipation of the analysis, so the fuel dilution factor isn't as critical as it appears.
It's a 1275 A+ bored to 1380 w/ 10:1 CR. A compression test shows 195 to 198 psi across the 4 cylinders, so I'm confident I don't have significant blow-by. The car's driven almost every day and always reaches operating temp. My twin SUs are in good order and my mass O2 gauge and spark plugs confirm I'm neither running too lean or too rich. Timing is spot-on.
The analysis also shows the oil viscosity is on the low side @ 100°C, but the lab says that's caused by the oil/gas dilution. Also, boron is as on the high side. Anyone know if boron is used in any critical engine/transmission parts? I use a carbon inhibitor fluid every couple of tank fulls—I'll check the label to see if boron is an additive.
Someone suggested that excessive fuel in the oil could be caused by too much fuel pressure and/or a leaky fuel float diaphragm. I have an electric fuel pump that I originally set to 2.5 psi. I checked it the other day and it's reading almost 4 psi. I also noticed that it takes almost 1 hour for the fuel pressure gauge to read zero after I've turned the engine off—plenty of time for fuel to leak past the diaphrams, right?
Questions:
1) Is 4 psi of fuel pressure enough to allow fuel to get past the diaphragm?
2) Is boron used in any critical engine/transmission parts? Bearings, bushings, valves/valve seats perhaps?