What "C" value to use in OCI formula for GC

[DeaconBlue]

I know that a UOA will give me a better reading, but I would like to at least use the OCI formula to calculate an approximate initial interval for using with my stash of green GC. I have seen several different "C" numbers quoted for GC in my searching on the BITOG site. What is the general consensuses of the "experts" here; 50, 60, 80, ?

For my '01 Buick Century with the 3.1L V6 engine using the larger PF-52 size filter, the formula looks like this;

mileage = (C)(26.2 MPG)(4.5 qrts)(187 ci) / 170 cHP rating

Since I also chart every single fill up with; date, mileage, trip od reading, gals, price and MPG rating per tank full, I can also use this formula as well;

gallons consumed = (C)(4.5 quarts)(187 ci) / 170 cHP rating

I have a 20 mile commute each way to work, of which 75% is on the highway, hence the good MPG readings over the past 5.5k miles or so. Since I have an ODB-II scan tool, I will also need to compare the results from the formula with what the OLM system has to say as well.

Thanks.

 

[DeaconBlue]

Thanks tooSlick. I have alrady had the intake gasket leak issue on the '00 3.4L, been lucky so far with the '01 3.1L. When I used a C value of 80 before in the formula, I was very surprised to see the 10K mile figure, which BTW GM says is the max interval for both these engines. I was thinking of trying the 6K/8K/10K step out UOA method would not be a bad idea, it made me feel good that you mentioned that

It's just that even the PF-52 is not that large of a filter, compared to say the FL-1 size. The 3.1L engines only see about 15K miles per year, so the old rule of thumb every 6 months or 7.5K miles could also be another option, but I was hoping to use a more technically sound method.

I will be interested to see what the OBD-II scan tool reads out from the OLM in the Buick. I have seen the OLM come on as quickly as 2.3k miles once with the the 3.4L in the wife's car - more short trips in the Winter I suppose. And yes I did remember to reset the system that time

 

[TooSlick]

I'd use a C* of 80 for the better API licensed synthetics like GC,M1,RP as well as the Amsoil XL Series. These are typically lubricants with TBN's in the 9.0-10.5 range

I'd be wary about running extended service intervals on the 3.1L/3.4L, GM engines unless it's supported by periodic oil analysis, due to their propensity for coolant leaks. A high TBN synthetic will give you better protection under these conditions, but the additives will be depleted significantly faster.

A C* of 80 would yield an OCI of approx 10k for this application. I'd test a few times after that interval to see how much margin you have left. A even more conservative approach would be to do a 6k/8k/10k "stepout", supported by analysis.

 

[AndyH]

TooSlick:

What do you think of the calculation for my STi running GC?

OCI mileage = (80)(18 MPG)(4.8 qts)(152.56 ci)/(325 HP)

I end up with an OCI of only 3,245 miles,

My intention was to run the GC out to a 5,000 mile OCI. Do you think I should cut it short at 3,000 for this first OCI and have it analyzed by Blackstone (I was going to use their services at 5,000 miles)?

Any thoughts would be appreciated.

Notes:

1) My car STi achieves an average of 18 MPG in my normal driving routine.

2) I have a Stage 1 ECU retune which bumps the HP up from 300 to 325.

3) The car sees mostly suburban street type driving, with a small bit of city and a bit of highway thrown in.

4) I drive aggressively, but do not abuse my car.

5) For the year that I've owned the car I've covered approx. 12,000 miles.

[ September 23, 2005, 08:38 AM: Message edited by: AndyH ]

 

[AndyH]

Forgot to add...

6) My daily commute to work is approx. 18 miles (36 mile round-trip).