# 20w50 ?



## Layzdude (Jun 14, 2015)

Just bought a 68 with a non original 400. Still trying to figure out the code so I can date the motor. PO told me the engine was rebuilt probably 5-6 yrs ago. It has a fairly heavy cam in it. He told me he used 20w50 non synthetic and that it does burn some oil. Not sure how much yet. Lol. Oil pressure is good. The car was in upstate NY and is now in central Jersey. My question is should I stay with the 50wt or switch to something lighter? 

Thanks.


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## BearGFR (Aug 25, 2008)

That's a really thick oil. My concern would be how hard it is to move that stuff through the engine on a cold startup, the most critical time for wear. A heavy oil like that is also going to result in a high oil pressure reading that may or may not have any basis in reality. Not knowing anything about what's really going on inside the engine or how it was built (clearances, etc) , I'd be hesitant to make a recommendation. What are your plans for it going forward?

Bear


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## geeteeohguy (Feb 2, 2008)

X2. 20/50 is pretty thick stuff. But, if you are already burning/using oil due to engine wear, thinner oil will burn off even quicker. You might try some 15/40 Rotella and see what happens.


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## 05GTO (Oct 6, 2004)

X3

I would also recommend a zinc additive if you're running flat tappet lifters. 

Welcome to the forum,


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## Layzdude (Jun 14, 2015)

Thanks for the responses. I was thinking the same thing about the oil being a little too thick for start ups. The PO did not have much info about the work done on the motor it was done by the person before him, supposedly a great Pontiac guy at the local dealer. Definitely has a heavy cam, not sure if flat or roller lifters (is their any way to tell without taking the motor apart?). Oil pressure reads about 75 at idle. As of not does not run hot. Thank goodness!!

Bear, My plans going forward...keep engine running as a driver. She needs full interior, then perfect motor and trans as both seem to work ok.


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## leeklm (Mar 11, 2012)

I am not Bob the oil guy, but as mentioned, 20w is way heavy for most street motors. Talking to different Pontiac specialists, most would suggest 10/30, 10/40 or 15/40 on the heavy end, along with a zinc additive if running a flat cam. Even though I have a roller cam, I still run a 1/2 bottle of GM EAS Lube (just for the warm fuzzies if nothing else) with house-brand 10/40. however, at $30 per bottle, you probably do not want to run EAS in a motor that leaks or uses oil!


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## Bensjammin66 (May 12, 2009)

Congrats on your purchase first of all and welcome to the forum! 

This article explains oil thermal dynamics in great detail.

Motor Oil Viscosity Grades Explained in Layman's Terms

The second number in a motor oil rating is relative to how it flows measured at 100 degrees C. The 'W' or winter rating is on a scale of extreme cold temps. "20w" is not twice as thick as 10w as some perceive, its more like 20-25% thicker. Which IS thick oil and it DOES take some added time to get to the top end. Warm the car up before giving it any real rpm and only use the 20w50 in real hot summer months like right now. Loose bearing clearance engines do like a thicker oil in the bottom end, also oil consumption may be slowed a little bit with a thicker oil. If the motor runs good and has good pressure with 20w50 next change go 10w40 and dont look back. Your modded 400 wont make enough constant extreme heat to break down 10w40 like a nitrous sprayed 12:1 461 stroker will. If the thicker oil is a band aid for low pressure thats all it is, a band aid. Time for bearings and head/valve work. 

By the way a little oil consumption is just fine in any engine regardless of what anyone tells you. The wifes 16k mile 38mpg 2014 EarthDreams 4cyl Accord even uses a little bit between changes. Have a good functioning PCV system in your car and run an inline air/oil separator between it and your carb base so your intake tract stays clean of blowby oil mist. Oil pressure is ok though? 10lbs per 1000rpm is the minimum you'll want to see.

Enjoy that Goat!!


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## Layzdude (Jun 14, 2015)

Thanks for the help. Been lurking on this site for years and recently got my first GTO, I finally have something to post about!!!


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