340k 5.7 Oil Weight Recommendations
#1
CF Veteran
Thread Starter
340k 5.7 Oil Weight Recommendations
Our 93 Sub has 340k on the original 5.7, only need to add a quart about every 2000 miles and runs fine. As expected, as it warms up, oil pressure drops. Starts off cold at 45psi or higher at idle. Once warmed up, holds 15psi at 60 mph, drops to 5psi or lower at idle -sometimes even triggers the check gauges light. Never any noises associated with the low pressure. So my questions are:
1. Original spec calls for 5-30 oil, should I change to 10-40 or 20-50?
2. Will increased viscosity increase pressure; but could this increase be harmful at cold motor start up?
3. And finally (here's ignorance on my part) I understand that the pressure drop is due to "wear and tear & increased tolerances" - but never have been given a satisfactory explanation as to why the pressure reads low if the oil pump is still pumping, and more importantly, if the oil is still flowing and lubing and no noises, does the low pressure really matter?
Thanks for your input, Red
1. Original spec calls for 5-30 oil, should I change to 10-40 or 20-50?
2. Will increased viscosity increase pressure; but could this increase be harmful at cold motor start up?
3. And finally (here's ignorance on my part) I understand that the pressure drop is due to "wear and tear & increased tolerances" - but never have been given a satisfactory explanation as to why the pressure reads low if the oil pump is still pumping, and more importantly, if the oil is still flowing and lubing and no noises, does the low pressure really matter?
Thanks for your input, Red
The following users liked this post:
Troy 93 k1500 (February 26th, 2022)
#2
1 quart in 2000 miles is not much considering.
for pressure to exist, you need restriction. As you have stated the tolerances are greater, so it only follows that the pressure drops.
a rule of thumb for oil pressure minimum specs is 10psi for every 1000rpm. if your above that, your ok.
you could test out the 10w oil for your oil pressure issue. I agree; concern for the 20w oil would be during cold winter start ups.
the only way to know where the issue lies is to check the pressure at the pump and at the sending unit.
Sounds like that truck has been fantastic.
for pressure to exist, you need restriction. As you have stated the tolerances are greater, so it only follows that the pressure drops.
a rule of thumb for oil pressure minimum specs is 10psi for every 1000rpm. if your above that, your ok.
you could test out the 10w oil for your oil pressure issue. I agree; concern for the 20w oil would be during cold winter start ups.
the only way to know where the issue lies is to check the pressure at the pump and at the sending unit.
Sounds like that truck has been fantastic.
Last edited by tech2; March 14th, 2015 at 9:38 PM.
#4
CF Veteran
Thread Starter
Thought I would update this since changing to 10-40. After a 30 minute freeway drive, pressure at 15-20 at 60-70 mph and more like 5-10 at idle vs former 5 or less. Also seems to jump to a higher pressure now when you get on the throttle more. So a little improvement and not triggering the check gauges light anymore. So should be ok for another 2-300k or so I guess as long as I have heavier wt oils to fall back on!!
#5
Super Moderator
I'd have no problem recommending the 20w-50w year round, if you just wanted to see more on the gauge.
Even in cold weather, with your "earned" clearances, there won't be a problem with a slow crank.
As stated, fantastic truck !
Even in cold weather, with your "earned" clearances, there won't be a problem with a slow crank.
As stated, fantastic truck !
Trending Topics
Thread
Thread Starter
Forum
Replies
Last Post
Mille Racer 69
Silverado, Sierra & Fullsize Pick-ups
12
April 12th, 2011 9:04 AM
Derek2023
Tahoe & Suburban
3
July 20th, 2007 5:34 PM