One aspect of VCT operation

[GMorg]

This was a passion of Jim Allen's for while, at least in modular fords. Maybe he will chime in.

I seem to recall that there is a temperature sensor in the loop (at least in fords) such that the system engages only after a certain temp has been reached. If so, that would go a long way towards explaining how the large range of viscosity that is associated with temperature can be tolerated.

 

[Garak]

Originally Posted By: 229
Techs have replaced thousands of cam phasers. Factory tells us that incorrect oil viscosity and filter shedding from non-OEM oil filters have caused the failures.


Filter shedding? It seems to me that dealerships and quick oil change places are the greatest offenders when it comes to installing the cheapest, most poorly made filters that money can buy.

 

[cp3]

How would the viscosity affect the phaser?

If the cam position sensors are used to determine how much advance or retard has been achieved why would the viscosity matter?

 

[Brettm1388]

"The CMP actuator assembly has an outer housing that is driven by an engine timing chain. Inside the assembly is a rotor with fixed vanes that is attached to the camshaft. Oil pressure that is applied to the fixed vanes will rotate a specific camshaft in relationship to the crankshaft. The movement of the intake camshafts will advance the intake valve timing up to a maximum of 50 crankshaft degrees. The movement of the exhaust camshafts will retard the exhaust valve timing up to a maximum of 50 crankshaft degrees. When oil pressure is applied to the return side of the vanes, the camshafts will return to 0 crankshaft degrees, or top dead center (TDC). The CMP actuator solenoid valve directs the oil flow that controls the camshaft movement. The ECM commands the CMP solenoid to move the solenoid plunger and spool valve until oil flows from the advance passage (11). Oil flowing thru the CMP actuator assembly from the CMP solenoid advance passage applies pressure to the advance side of the vanes in the CMP actuator assembly. When the camshaft position is retarded, the CMP actuator solenoid valve directs oil to flow into the CMP actuator assembly from the retard passage (3). The ECM can also command the CMP actuator solenoid valve to stop oil flow from both passages in order to hold the current camshaft position."

This is GM SI. It is my understanding that the oil is only used in a type of hydraulic fluid, and thus, I don't see where viscosity is much of a factor. I wouldn't go using 20w-50 if its 0 degrees outside but, that applies to most any engine.
And yes, it does have a TSB for filters and we have seen so far, 3 Frams, 1 Service Champ, and 1 Amsoil Filter cause engine failure.

 

[GMorg]

I don't know that viscosity does affect the phaser. However, OEMs seem to be making that claim. It seems that since the system operates on OP and the flow of oil through the control valves, then if pressure or flow are outside of design parameters, then the function of the system may be out of spec. Since the PCM controls of the duty cycles on the VCT actuator/solenoid and those controls may be dependent on assumptions about pressure and flow rate, then cam positioning may be inappropriate at any one time. Since the PCM is also controlling air flow, timing, and fuel delivery, there could be inappropriate adjustment made to compensate for the inappropriate cam phasing. In the end, as the argument goes, the overall system under performs, throws codes, and can cause issues related to fuel/air management and timing, knocking or carbon build-up for example.

The paragraph above could be a complete myth. I know that I don't know if viscosity is VCT issues. I am trying to figure out if there is a plausible basis in reality for the hysteria surrounding SAE grade and newer engines.

All I know for sure is that I miss the days of engines being mechanical in nature instead of electronic.

 

[OVERKILL]

GMorg:

Well, both Ford and BMW at least don't appear to have any concerns regarding the viscosity of lube used in their systems. They have apps spec'ing 5w20 (Ford) and 5w50 (Ford) as well as 5w30 (BMW) and 10w60 (BMW).

Ford even had a TSB regarding noisy phasers and the user simply switching to 10w40 to alleviate.

Perhaps "at temp" certain systems are more sensitive than others? But that means you have to completely ignore the massive warm up curve a lubricant goes through, particularly in winter when you are talking THOUSANDS of cSt in terms of viscosity change, versus the very minor variances between the actual SAE grades themselves.

 

[cp3]

Originally Posted By: GMorg
I don't know that viscosity does affect the phaser. However, OEMs seem to be making that claim. It seems that since the system operates on OP and the flow of oil through the control valves, then if pressure or flow are outside of design parameters, then the function of the system may be out of spec. Since the PCM controls of the duty cycles on the VCT actuator/solenoid and those controls may be dependent on assumptions about pressure and flow rate, then cam positioning may be inappropriate at any one time. Since the PCM is also controlling air flow, timing, and fuel delivery, there could be inappropriate adjustment made to compensate for the inappropriate cam phasing. In the end, as the argument goes, the overall system under performs, throws codes, and can cause issues related to fuel/air management and timing, knocking or carbon build-up for example.



This is along the same lines I was thinking originally. Made sense to me that a different viscosity may (not a fluid dynamics expert) cause the volume of oil put into the phaser to change, higher pressure=more volume per second? That being correct or not, it doesn't make sense as it would have to be a predetermined value and I think it would be easier for the ECM to monitor cam position and make adjustment based on that.

 

[Highline9]

I can only speak to Chrysler and their VVT/MDS setup, which is oil driven.

There has been much ado over the oil spec since 2004. It is complete bunk, as thousands of Hemi owners have discovered that all thicker oil does is change the operation very slightly, if at all.
20w, 30w, 40w, and even 50w work just fine.

I can vouch for that +1

 

[dave1251]

Originally Posted By: OVERK1LL
GMorg:

Well, both Ford and BMW at least don't appear to have any concerns regarding the viscosity of lube used in their systems. They have apps spec'ing 5w20 (Ford) and 5w50 (Ford) as well as 5w30 (BMW) and 10w60 (BMW).

Ford even had a TSB regarding noisy phasers and the user simply switching to 10w40 to alleviate.

Perhaps "at temp" certain systems are more sensitive than others? But that means you have to completely ignore the massive warm up curve a lubricant goes through, particularly in winter when you are talking THOUSANDS of cSt in terms of viscosity change, versus the very minor variances between the actual SAE grades themselves.




"Ford even had a TSB regarding noisy phasers and the user simply switching to 10w40 to alleviate."

This will be my argument that visocity will have very little effect on VCT.

 

[mechtech2]

One consistently faulty piece from one mfr is not an oil problem, it is a design problem that can be attenuated with oil.

 

[SteveSRT8]

^^^^Bravo^^^^

That was short sweet and concise.

 

[GMorg]

I'll bite mechtech2. Through what mechanism can oil viscosity attenuate this design flaw?

It seems that if an oil can attenuate a design flaw, then it can matter in a slightly less flawed design too.

 

[SHOZ]

My Hyundai Genesis Coupe has dual cam VVT. They also recommend oil from 5w20 to 10w40. But until the oil temp is 140F it does not open the solenoids.