UOA shows dilution. Help diagnose the source

I got my first UOA report at the end of last week. Wear metals all look excellent. Dilution though is a concern. TBN for the Amsoil European 5w-40 that I'm running is 8 and in just over 5k I'm down to 2.85. Hot engine viscosity is down but within 30-weight standards. Dip stick reads just slightly below full so consumption is minimal. It looks like I need to at least drain down a quart or 2 and refill to boost my viscosity if I don't just drain everything and start over but I'll still have the dilution issue.

Since I do a lot of highway miles and don't sit idling very much at all, my Amsoil rep suggests 3 possible sources of the excess fuel in the oil. Failing injector(s), bad plugs, or bad plug wires. I changed the plugs only about 20k ago and the plugs I took out looked pretty good for having 60,000 miles on them. I didn't notice the coil pack wires looking poorly when I was fiddling with the packs to change the plugs. So my first suspect of those 3 would be injector(s).

Are there other possible sources for the dilution and short of taking it to my dealer are there ways I might be able to at least get a better idea of where I might have a problem?

Plugs and wires don't have to look bad to perform poorly. When you changed the plugs did you go with the recommended NGKs or something else?

Sounds like you are around 80k miles. I agree that your injectors may be a culprit, though I'm surprised if you are getting excess fuel in a cylinder that you're not seeing any other issues. Any stumbles if you go WOT from say 1500 rpm to redline under load? No driving difference when it is hot vs. when it is cold? You may have to do some off-highway time. Also, I'll vote against running injector cleaner or seafoam.

How many miles on the injectors? May be worth pulling them and sending them off for cleaning/flow balancing.

My guess is that they could be original so that would give them 140,000 miles. This is our only car so having it down for an extended time could be problematic. Recommendations on finding a place qualified to clean/balance them? Or at that age should I just bite the bullet and replace them instead? I'm not looking to upgrade them or this would be a good excuse for that.

Plugs and wires don't have to look bad to perform poorly. When you changed the plugs did you go with the recommended NGKs or something else?

 

Sounds like you are around 80k miles. I agree that your injectors may be a culprit, though I'm surprised if you are getting excess fuel in a cylinder that you're not seeing any other issues. Any stumbles if you go WOT from say 1500 rpm to redline under load? No driving difference when it is hot vs. when it is cold? You may have to do some off-highway time. Also, I'll vote against running injector cleaner or seafoam.

What's the best way to check the coil packs and wire harness for them? I put in the specified NGK's. Making all that effort to change them I felt it best to go with the best. I haven't noticed any other symptoms but I seldom get anywhere near redline so maybe haven't had an opportunity for the situation where they would manifest. The only possible anomaly I have detected is an occasional slight roughness at idle but this isn't a consistent situation nor is it ever really obvious.

I've heard of some issues with Seafoam so have been skeptical of putting that in. I have however used the Amsoil Performance Improver. The first bottle was added at 134,306 and I switched to this oil change at 134,494 right near the end of that tank of gas. I waited until after I pulled the sample for the UOA before using it again. I did see about a 2 mpg improvement about the time of the first use but there were other things I did about the same time (upgraded oil, new rear wheel bearings, new tires) so there could have been a cumulative effect.

I really appreciate the input.

I got my first UOA report at the end of last week. Wear metals all look excellent. Dilution though is a concern. TBN for the Amsoil European 5w-40 that I'm running is 8 and in just over 5k I'm down to 2.85. Hot engine viscosity is down but within 30-weight standards. Dip stick reads just slightly below full so consumption is minimal. It looks like I need to at least drain down a quart or 2 and refill to boost my viscosity if I don't just drain everything and start over but I'll still have the dilution issue.

 

Since I do a lot of highway miles and don't sit idling very much at all, my Amsoil rep suggests 3 possible sources of the excess fuel in the oil. Failing injector(s), bad plugs, or bad plug wires. I changed the plugs only about 20k ago and the plugs I took out looked pretty good for having 60,000 miles on them. I didn't notice the coil pack wires looking poorly when I was fiddling with the packs to change the plugs. So my first suspect of those 3 would be injector(s).

 

Are there other possible sources for the dilution and short of taking it to my dealer are there ways I might be able to at least get a better idea of where I might have a problem?

I'm confused, could you post the actual report? Did the report say there was fuel dilution present? Or do think theres fuel dilution because of the tbn retention? Lowered viscosity could be from fuel dilution, but it could also be from shear, especially in these cars. What was the flashpoint of the used oil?

Makes me wonder whether your O2 sensor may be bad (going) so it's running overly rich all of the time. How's your MPG mileage?

Looking at the car's computation, which I think is optimistic, more recently I get in the ballpark of 24 on the highway and 22 combined. Back before 6k miles ago it was about 2 mpg worse since the whole 2 years I've had the car. It was at least as good as our previous '99 OB but I never considered it all that good but chalked it up to AWD.

I'm confused, could you post the actual report? Did the report say there was fuel dilution present? Or do think theres fuel dilution because of the tbn retention? Lowered viscosity could be from fuel dilution, but it could also be from shear, especially in these cars. What was the flashpoint of the used oil?

I'll make an attempt later tonight or tomorrow to post the report. The report did say that fuel dilution was an issue. It listed it at 1.6% and my Amsoil rep said that 2% and above is considered abnormal. I don't see flashpoint as something that was quantified.

UOA report.pdf

At only 1.6% fuel dilution, I wouldn't be too concerned. If you do lots of short trips or didn't get your oil up to operating temperature before taking the sample, then you may have higher than normal amounts of unburned fuel in the sample.

At the time I took the sample the car had been driven a mix of mostly locally and longer trips for the previous few weeks. The week before the test consisted of a trip of 220 miles on Monday and Thursday with local driving on the 2 days between. The morning of the test I took my daughter to her flute lesson about 10 miles away and then took the sample after we returned. So unfortunately neither of the conditions you mention as possible causes for the dilution seem to be the case at least in the immediate past leading up to the test.

I guess my concern stems from the fact that I was wanting to go to 10,000 mile OCI with this oil and at 5k the viscosity has already dropped to approximately 30 weight. Since I drained and replaced 2 quarts, now I'm in the process of considering if there would be any value with another UOA at about 8500-9k or should just change everything and start over.

Or...

You could realize it's a turbo 4 and not a 16L diesel and just change the oil at 5k with synthetic and not get any UOA. A $15 UOA is at least 2.5 quarts towards the next oil change.

Or...

 

You could realize it's a turbo 4 and not a 16L diesel and just change the oil at 5k with synthetic and not get any UOA. A $15 UOA is at least 2.5 quarts towards the next oil change.

^ What he said. 10k is a ridiculous OCI for a turbo'ed Subaru, I don't care how awesome the oil is.

I hold some agreement with both of you. I would not even consider the 10k OCI without the UOA and wanted a benchmark well before that. But as pointed out, the money that goes toward the UOA could buy a decent portion of the oil. I probably would have stayed with the Amsoil OE and 3750 OCI but AZPInstalls has seen good results and no problems with numerous of his turbo Subaru clients using the Amsoil European on 10k intervals. Under normal circumstances it's not unusual for me to put 3000 miles on the car in a little over a month so was trying to get a little more breather in between changes. Maybe it's just not worth it in dollars, sense and peace of mind.

I don't care what shop you go to, you will NOT find a correlation between what brand/type/weight of oil and engine failures.

As long as you have oil in your car and it's not worn out, a failure is probably not the oil's fault.

A couple weeks ago I had just hit 7500 miles on this change of oil and with the dilution indication and a couple long trips coming up I didn't want to take a chance on stretching the oil beyond its functional life so I changed it. But before I did I took another sample and sent in in for another analysis just to see what had transpired since the first UOA and my drain and refill of 2 fresh quarts. The first sample had been taken after I got back from a trip of about 20 miles total round trip with a 30 minute break in the middle. This time I had just finished my 220 mile trip home from work. The results were very interesting. Despite the added mileage on the oil the dilution had gone from 1.6 down to 1.2 and the 100 degree C viscosity and base numbers were both better as well. Overall the condition rating changed from abnormal 3 to a better abnormal 2. The service recommendation was to top off, change the filter and check again in 3500 miles.

I would guess that this might indicate that a more accurate reading might be obtained by taking the sample after the engine has run a while rather than after a short, first trip of the day. It's probably also an indication that a series of analysis reports will give a better picture of what's going on and indicate better what is an anomaly vs. consistent conditions. I've got another prepaid test so will probably do another analysis when this change gets around 5k on it.

I would guess that this might indicate that a more accurate reading might be obtained by taking the sample after the engine has run a while rather than after a short, first trip of the day. It's probably also an indication that a series of analysis reports will give a better picture of what's going on and indicate better what is an anomaly vs. consistent conditions. I've got another prepaid test so will probably do another analysis when this change gets around 5k on it.

That is correct, you don't want to drive your car short distances and shut it off. Long drives are better for the oil.

I have decided to go with 5000 mile OCI on both my cars, using Amsoil European 5w-40 and there filters. If I did a OA and paid the $35.00 for that...+ postage, I figure, I'll just put that money towards the next oil change, and be safe.

Max, that's what I'm running after hearing nothing but good things about Amsoil. I'm coming up on the 5k mark, and I'm going to run a UOA just for kicks 'n giggles to see how it stacks up against the M1 0w40 and GC I've run in my car.

I checked the oil the other day and it still looks blonde which means the filter is doing its job nicely.