Does oil affect evaporative emissions control pressure inside the engine?

[Nyyt]

A little background, I have a bluetooth dongle for the odbII port on both my 2008 Odyssey and 2009 Honda Fit. Using Torque on my android I have it log 10 or so sensors. The evap pressure with PUP, Quaker State UD, and Valvoline fluctuated wildly in both vehicles. The last oil change on both was a 50/50 mix using redline 0w-20 and 10w-30, and I noticed it didn't change much in similar driving conditions and weather conditions. Then with the last change I did a 50/50 Motul 8100 5w-30/Amsoil 0w-20 in the fit and a 50/50 mix of the same motul the fit received and mobil1 0w-20 EP in the odyssey. I notice the evap pressure remained fairly consistent, with little variation, unlike the other oils tried, which touched off my curiosity.

On a side note, my odyssey tells me when to change the oil without the OLM telling me. At about 3000 miles it throws the check gas cap code until the oil is changed. After oil change, reset the code, and voila wait another 3000 miles. It's a bizarre issues I've been puzzling on. I put a vcmtuner on it a couple weeks ago so this will be the first oil change after putting it on but the early results are showing no oil usage in 1k miles which is a blessing.

Thanks

 

[AmirKhat007]

Seems like a strange issue there, the oil is an essential part of sealing the compression chamber which of course prevents the crankcase pressure from rising out of control. I'm not quite sure what could be causing this issue honestly, but I'd say I've never heard of a case where the manufacture suggests different weight oils like that therefore, using the same weight oil might be a good place to start in pinpoint the issue.

 

[kschachn]

Seems like a strange issue there, the oil is an essential part of sealing the compression chamber which of course prevents the crankcase pressure from rising out of control. I'm not quite sure what could be causing this issue honestly, but I'd say I've never heard of a case where the manufacture suggests different weight oils like that therefore, using the same weight oil might be a good place to start in pinpoint the issue.

I'm unsure what connection there is between the crankcase pressure and the evaporative (fuel tank) pressure.

Overall I can't draw any connection between motor oil and the evaporative system. Evaporative system pressure is normally going to fluctuate due to temperature and operation of the vehicle and it will fluctuate during the startup testing sequence. This whole thread is making connections that don't exist on the vehicle.

 

[AmirKhat007]

You're right its normal for the evaporative pressure to fluctuate. Sorry, I didn't specify how they could be correlated, their both usually plumed into the same intake tubing, therefore excessive crank case pressure could be causing fluctuations in the EVAP system, you may want to also check your air filter as this could be exasperating things.. I'd look at the PCV line to see if there's excessive blowby with the different oils.. admittingly this theory is a bit of a longshot.

 

[kschachn]

You're right its normal for the evaporative pressure to fluctuate. Sorry, I didn't specify how they could be correlated, their both usually plumed into the same intake tubing, therefore excessive crank case pressure could be causing fluctuations in the EVAP system, you may want to also check your air filter as this could be exasperating things.. I'd look at the PCV line to see if there's excessive blowby with the different oils.. admittingly this theory is a bit of a longshot.

That could only be a problem if there was an inoperative or leaking purge or vent valve, and if that were the case there would be a diagnostic code. The OP is only viewing normal pressure differences in the system at different times and different phases of operation and none of that has anything to do with the engine oil being used.

His intermittent gas cap code worries me more than anything else, that might be an indication of a problem with something else in the system. That's far more likely to be the problem causing pressure fluctuations, assuming there is one in the first place. Whatever the case it is not the oil.

 

[mpgo4th]

Is this a cap less fuel system? If so they do stick and cause pressure fluctuations. Evap is indeed a fuel pressure system to vent pressure/fumes out of the tank without putting it straight into the atmosphere. They use one way check valves and solenoids to control the ventilation. One would have to be open or failed to change pressure. If there was a problem like that present it would definitely set a check engine light.

 

[Nyyt]

I'm unsure what connection there is between the crankcase pressure and the evaporative (fuel tank) pressure.

Overall I can't draw any connection between motor oil and the evaporative system. Evaporative system pressure is normally going to fluctuate due to temperature and operation of the vehicle and it will fluctuate during the startup testing sequence. This whole thread is making connections that don't exist on the vehicle.

Please don't assume I'm trying to make any connections. I made an observation, asked a question to those who are smarter than I am, and I got the answer it doesn't correlate - curiosity satisfied, its how I learn. Working in IT for the past 20 years has made me attuned to patterns which I'm able to hunt down, with cars I'm still learning and growing, so please be gentle.

 

[Nyyt]

That could only be a problem if there was an inoperative or leaking purge or vent valve, and if that were the case there would be a diagnostic code. The OP is only viewing normal pressure differences in the system at different times and different phases of operation and none of that has anything to do with the engine oil being used.

His intermittent gas cap code worries me more than anything else, that might be an indication of a problem with something else in the system. That's far more likely to be the problem causing pressure fluctuations, assuming there is one in the first place. Whatever the case it is not the oil.

I've been hunting it down the gas cap code for a year now. Replaced the pcv valve 7 months ago, removed the egr valve and cleaned it, someone on the odyssey forums suggested that since he had a gummed up one that would throw the pcode. It usually happens when the tank is near empty and the ambient temperature changes more than 10 or so degrees.

 

[kschachn]

Neither the PCV valve nor the EGR valve is going to affect a gas cap code. You're still chasing ghosts in entirely the wrong system. It would be like a plumber telling you the bath drain was clogged and you replace the light bulb in the refrigerator.

Have you tried a new OEM gas cap? If not that then the next step is examine all the hoses in the evaporative system. But with a specific cap code that's where you begin.

 

[Nyyt]

Neither the PCV valve nor the EGR valve is going to affect a gas cap code. You're still chasing ghosts in entirely the wrong system. It would be like a plumber telling you the bath drain was clogged and you replace the light bulb in the refrigerator.

Have you tried a new OEM gas cap? If not that then the next step is examine all the hoses in the evaporative system. But with a specific cap code that's where you begin.

Sorry, the first thing I did was replace the gas cap, forgot to put that in there.