2010 Jetta TDI Sportwagen 6500 mile UOA - 8% FD - RLI HD 10w30

[CleverUserName]

High fuel dilution @ 8%. This car has a bad thermostat which I found by watching coolant temp PIDs with my Maestro equipped pioneer receiver. It was also doing excessive DPF regenerations every 180 miles. I think the excess fuel and regenerations is from the low coolant temps causing the ECU to run in open loop. This car has no stored or active codes which is rare for a VW. No other diagnostic work has been done yet.

If anybody has another theory of what is happening here, chime in. The backstory in the car is below:

I got this low mileage Jetta sportwagen in April 2020 when covid-19 was in full swing. It was really cheap, the original owner who was in his ‘80s died in 2018 and it had been sitting for about 1 year. Rodents did some damage to the wiring which was repaired by the dealership.

I bought it with 46k miles for $6800 from the attorney managing the estate. It was about 200 miles away, however I contacted him first and he held it for a few days. It is a 6 speed manual without a sunroof (VW sunroofs can have issues) which is what I was looking for. It was in VG condition with a couple body imperfections. It was a major PITA to get this thing titled in my name as the DMV was shut down.

This is the first UOA, I haven’t driven it much because I could tell it had some issues. It’s down now, getting a bunch of work done including a CR170 Turbo, sport suspension including Eibach coil-overs, new Sachs SRE clutch/timing belt/fluidamper/accessory belt/WP etc... to much to list here.

I added the lightweight wheels and Michelin Pilot Sport A/S 4 tires in 235/45R17. I also had the maestro equipped pioneer avic-w8500-Nex receiver and pioneer backup camera installed

 

[xgmad]

Nice car, its been taken care of. Change the thermostat lol

 

[incognito_2u]

Maybe I missed it, but how many miles and how long was the interval on this Oil?
Also, was the oil changed after you took possession of the vehicle?

 

[CleverUserName]

Maybe I missed it, but how many miles and how long was the interval on this Oil?
Also, was the oil changed after you took possession of the vehicle?

Yes I changed the oil soon after I got it about a year ago. That’s why it has Biosyn HD 10w30 in it LOL. Glad I put it in because it handled the FD like a champ.

The mileage is in the thread title and the report itself. Approximately 6500 miles on the oil and the car now has 53000 miles total. It’s not being driven until the work gets completed including an oil change.

 

[kschachn]

Yes I changed the oil soon after I got it about a year ago. That’s why it has Biosyn HD 10w30 in it LOL. Glad I put it in because it handled the FD like a champ.

The mileage is in the thread title and the report itself. Approximately 6500 miles on the oil and the car now has 53000 miles total. It’s not being driven until the work gets completed including an oil change.

I don’t understand how one oil could “handle” fuel dilution better than another? Isn’t it simple dilution of a higher viscosity fluid with one that’s lower? Aside from moving up a grade how would one oil handle it better than another?

 

[CleverUserName]

I don’t understand how one oil could “handle” fuel dilution better than another? Isn’t it simple dilution of a higher viscosity fluid with one that’s lower? Aside from moving up a grade how would one oil handle it better than another?

You should read the old threads about Biosyn and the RS4 with extreme fuel dilution. This is ancient BITOG going back to 2008-ish. Terry Dyson was involved with it. Something about the Biosyn chemistry that resists fuel dilution. It’s also a high density lubricant which also helps. It was still a 30 wt even with 8% FD so it did its job as far as I’m concerned.

 

[kschachn]

You should read the old threads about Biosyn and the RS4 with extreme fuel dilution. This is ancient BITOG going back to 2008-ish. Terry Dyson was involved with it. Something about the Biosyn chemistry that resists fuel dilution. It’s also a high density lubricant which also helps. It was still a 30 wt even with 8% FD so it did its job as far as I’m concerned.

Yeah okay.

 

[CleverUserName]

Yeah okay.

Not sure if you’re being sarcastic, but to ignore the data, time and $$ spent on research individuals contributed many years ago is a disservice to this site.

You can ready these threads, there are more if you dig deeper. Enter this into google: RI_RS4 and biosyn site:bobistheoilguy.com

I have used Biosyn HD in 10w30, 15w40 and a blend of the two since 2016 in all of my diesel vehicles. It has always given me low wear metals and maintained oil pressure/viscosity better than the hydrocarbon based synthetic oils in the presence of FD.

It is impressive that I had 8% fuel in the sample, yet still maintained the viscosity and had normal metal wear rates for a CR 2.0 TDI.

 

[kschachn]

If you’re convinced of it there’s not much I can say. That’s what I meant.

For me however I will still stick with the physics of mixing fluids with different viscosities.

 

[Okcafe]

Goodness. Personally Id cut OCI in half and run another UOA. In the meantime Id be looking at live data/fuel trims, o2 sensors, maf etc.

 

[Popsy]

For me however I will still stick with the physics of mixing fluids with different viscosities.

Isn't fuel affecting some VI more than others? This is a real question.
Not sure about diesel vs gas.

 

[CleverUserName]

Goodness. Personally Id cut OCI in half and run another UOA. In the meantime Id be looking at live data/fuel trims, o2 sensors, maf etc.

I’m not driving the car. It’s getting a bunch of upgrades and maintenance done, including more diagnostics.

I think the FD is from the excessive DPF regens due to the thermostat that’s failed open.

 

[Jetronic]

Diesels don't run in closed loop as gas engines do, and diesel fuel doesn't evaporate from oil like gas does. Excessive regenerations will increase the fuel dilution significantly though. What's the cause for the frequent regenerations? I'm a bit p***** off if I get a regeneration within 600 miles from the last one...

 

[CleverUserName]

Diesels don't run in closed loop as gas engines do, and diesel fuel doesn't evaporate from oil like gas does. Excessive regenerations will increase the fuel dilution significantly though. What's the cause for the frequent regenerations? I'm a bit p***** off if I get a regeneration within 600 miles from the last one...

This car supposedly got updated software and new DPF in 2018 as part of the VW dieselgate settlement modifications. Right before I got it, about 10k miles ago.

The regenerations always happen every 180 miles regardless of driving cycle. I don’t have a soot load PID to view on my receiver, however I don’t think it’s being triggered by actual soot load. I think 180 miles, it’s some kind of default value which my theory was an open loop condition.

The only indication that there is something wrong is the low coolant temps, which are usually 160-170F. VCDS shows no faults

 

[kschachn]

Isn't fuel affecting some VI more than others? This is a real question.
Not sure about diesel vs gas.

If true that would make it worse, not better.

 

[Jetronic]

That could be but it's extremely conservative (180 miles between regens). Diesels put little heat into coolant compared to gas engines, especially at speed. combined with the generally bigger radiators to expell heat at low rpm, they tend to run with the thermostat barely cracked open. So 160-170 might not be in error. Coolant temps will go up when the engine get loaded though.

Just to add, I know of some users that get regens faster than 180 miles even though there's nothing wrong with their cars, it's all due to the driving conditions. So it doesn't have to be a problem, besides the fuel dilution and extra fuel use..

 

[CleverUserName]

That could be but it's extremely conservative (180 miles between regens). Diesels put little heat into coolant compared to gas engines, especially at speed. combined with the generally bigger radiators to expell heat at low rpm, they tend to run with the thermostat barely cracked open. So 160-170 might not be in error. Coolant temps will go up when the engine get loaded though.

Just to add, I know of some users that get regens faster than 180 miles even though there's nothing wrong with their cars, it's all due to the driving conditions. So it doesn't have to be a problem, besides the fuel dilution and extra fuel use..

I have more than one diesel vehicle, I’m aware they are more thermally efficient than gasoline engines. However the thermostat should be shut until ~ 190F. The coolant temp has never gotten that high. Ever. Even under constant load driving on the freeway. The highest it’s been is 180-ish in traffic or driving slow speeds. This car has a working EGR cooler so there should be some additional heat transfer to help it maintain temperature as well but it never does get to where it needs to be. During our mild winters, turning on the heater would also drop the coolant temps even lower. You could see it happening in real time.

 

[Jetronic]

if it drops lower you're right the thermostat is likely stuck open. But in all they do tend to run cooler than usual compared to gas engines

 

[andreigbs]

FWIW, my last TDI (2014 Jetta post-fix) would run quite high coolant temps especially in Chicago traffic. My ScanGaugeII was showing coolant temps into the low 200s *F. It was also running a regen seemingly every couple hundred miles, and I hated it.

The regen cycle is part of the "fix" VW was forced to make, which resulted in many a cracked DPF from heat stress fatigue. Telltale sign would be soot on the rear bumper. Luckily my 200-mile daily commute pre-COVID was mostly interstate and high speeds, but it made no difference to the regen cycle. To compare, my Bluetec would run regens every 650 miles or so. On roadtrips, it would even stretch it to 800+ miles before initiating.

The more often regens run, the more fuel dilution is likely to happen. As a result, I don't think it's safe/wise to run a 10k miles OCI as before, even with a 504/507 spec oil. Perhaps a high-quality HDEO would protect the engine better against fuel dilution issues?

 

[CleverUserName]

FWIW, my last TDI (2014 Jetta post-fix) would run quite high coolant temps especially in Chicago traffic. My ScanGaugeII was showing coolant temps into the low 200s *F. It was also running a regen seemingly every couple hundred miles, and I hated it.

The regen cycle is part of the "fix" VW was forced to make, which resulted in many a cracked DPF from heat stress fatigue. Telltale sign would be soot on the rear bumper. Luckily my 200-mile daily commute pre-COVID was mostly interstate and high speeds, but it made no difference to the regen cycle. To compare, my Bluetec would run regens every 650 miles or so. On roadtrips, it would even stretch it to 800+ miles before initiating.

The more often regens run, the more fuel dilution is likely to happen. As a result, I don't think it's safe/wise to run a 10k miles OCI as before, even with a 504/507 spec oil. Perhaps a high-quality HDEO would protect the engine better against fuel dilution issues?

Yeah 190-200F is normal for coolant temps. I know the thermostat is stuck open.

I'm aware of the cracked DPFs, I don't have any of those issues. From what I read, 180-300 miles is normal between regens on a "fixed" CJAA. Mine does it only at 180 miles regardless of how much freeway driving I do.

It didn't have 507 in it. 10w30 CJ-4.