cSt? pennzoil platinum 10w30 too thick?

[sparkplug619]

I have been studying oil for about 3 hours today in this section and countless hours over the past week.

When I did an oil change the other day, I put in pennzoil platinum 5w20, a fellow member told me it was too thin for an old engine and recommended a 10w30

I then checked the oil viscosity chart and checked all the oils available in my area. I then decided to stick with the pennzoil platinum but changed the weight to 10w30. the cSt rating for that is 63.4 at 40 celsius and 10.5 at 100 celsius, compared to the castrol "GC" 66.8 at 40 celsius and 12.1 at 100 celsius. Does that mean my oil is thicker or thinner then the "gc".

Based on what I have read on other sites, the lower the cSt you get at each temperature, the more flow you will get because the cSt is based on the time it takes to circulate! Is this correct?

Now people are telling me I went too thick. I am completely confused. I hate to admit it but I caused rod knock on my old supra because I went with an extremely thick oil and I am trying to be extra cautious now.

 

[jdub]

Pennzoil Platinum 10W-30 is not too thick...in fact, it is an excellent choice for the 7M. If you get the TSRM pressures at idle/3000 RPM, use it and be happy.

A 5W-20 on the other hand is too thin IMO. However, it's been used with success in this motor...if you do use a 20W oil, I would do so only in an engine that has the stock filter head removed and a full flow T-stat controlled oil circuit installed with a cooler at least twice stock size. You do not want the oil to overheat using a 5W-20 and cause a drop in viscosity. There is little room for to compensate for hot oil temps.

Oil viscosity is how well it flows. The only impact time has is how quickly it gets to a 100 deg C ops temp. The most wear on a stock engine occurs at cold start...oil does not flow as well cold (it's thicker). If you run the motor hard cold (especially using a thick oil), you can starve the bearings of the flow required.

 

[sparkplug619]

So what I read about is false? cSt is not determined by how long it takes to circulate?

Thanks for the info, its really appreciated

 

[jdub]

Only in the sense of the amount of time that oil circulation warms it up to ops temp. Oil always gets thinner as it gets hot. The "cold" specs you listed above are at 40 deg C, that's 104 deg F.

Once the oil in your motor achieves the above temp it will continue to thin to the 100 deg C spec, and the decrease in viscosity will continue above 100 deg C if temps are allow to increase. That is why a good cooler is important...it is an excellent case for dumping the stock pressure based cooler circuit for a full flow T-stat controlled cooler circuit. It keeps the oil at the 100 deg c spec much better and gets rid of the pressure bleed associated with the stock set-up.

BTW - you're welcome...it's nice to see a guy that does a bit of research 1st and then asks questions