I know how much you guys like sludge pics so...
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Originally Posted By: joegreen
...I have put at least 3000 miles on the truck since i bought it and all seems well...
That's all that matters.
Might want to get those leafs squared away though!
...I have put at least 3000 miles on the truck since i bought it and all seems well...
That's all that matters.
Might want to get those leafs squared away though!
Originally Posted By: joegreen
I use valvoline 80w90 in both diffs. But what's wrong with 75w90?
Originally Posted By: joegreen
Here is what it looks/looked like under the valve cover on my 78 chevy k20 with a 350 sbc. I know nothing about the maintenance history of the vehicle but im sure it was not good. It was mostly a yard plow truck I think.
The long answer ........
Assuming this 1978 truck owner manual specifies differential gear oils grade at SAE 80W90 / SAE 90 mineral oils for cold ambients and SAE 85W140 / SAE 140 for warm/hot ambients in the good old days.
However in late 1990's , the 'Former 90' viscosity gear oil SAE J306 classifications was revised to further differentiate its viscosity range ratings and split into two categories,namely :
a )the 'Current SAE 90' grade of AGMA 4EP/ ISO 150 classifications (KV@40*C 135 to 165 cSt) ,refer LE 1604 below http://lubetechnologies.com/assets/1601-1610-product-info.pdf , and
b )a 'New SAE 110' grade of AGMA 5EP / ISO 220 classifications (KV@40*C 198 to 242 cSt), refer grade LE 1605 in (a) above.
Now most current day 75W90 have KV@40*C of 100ish cSt , which falls into AGMA 3EP / ISO 100 (KV@40*C 90 to 110 cSt) , refer
https://www.amsoil.com/lit/databulletins/g2043.pdf
http://www.redlineoil.com/product.aspx?pid=133&pcid=4
As most automotive differentials 'tends' to operate at a temperature range of 55*C (135*F) and 70*C (160*F), an AGMA 3EP / ISO 100 gear oil generally provides weaker oil film strength than an owner manual spec'ed pre-2000 SAE 90 gear oils, offering lower wear protection to differential gears and bearings.
JMHO.
Note:A plowing/towing truck requires increased oil film strength against components wear protection.
Thank you for your patience ...
I use valvoline 80w90 in both diffs. But what's wrong with 75w90?
Originally Posted By: joegreen
Here is what it looks/looked like under the valve cover on my 78 chevy k20 with a 350 sbc. I know nothing about the maintenance history of the vehicle but im sure it was not good. It was mostly a yard plow truck I think.
The long answer ........
Assuming this 1978 truck owner manual specifies differential gear oils grade at SAE 80W90 / SAE 90 mineral oils for cold ambients and SAE 85W140 / SAE 140 for warm/hot ambients in the good old days.
However in late 1990's , the 'Former 90' viscosity gear oil SAE J306 classifications was revised to further differentiate its viscosity range ratings and split into two categories,namely :
a )the 'Current SAE 90' grade of AGMA 4EP/ ISO 150 classifications (KV@40*C 135 to 165 cSt) ,refer LE 1604 below http://lubetechnologies.com/assets/1601-1610-product-info.pdf , and
b )a 'New SAE 110' grade of AGMA 5EP / ISO 220 classifications (KV@40*C 198 to 242 cSt), refer grade LE 1605 in (a) above.
Now most current day 75W90 have KV@40*C of 100ish cSt , which falls into AGMA 3EP / ISO 100 (KV@40*C 90 to 110 cSt) , refer
https://www.amsoil.com/lit/databulletins/g2043.pdf
http://www.redlineoil.com/product.aspx?pid=133&pcid=4
As most automotive differentials 'tends' to operate at a temperature range of 55*C (135*F) and 70*C (160*F), an AGMA 3EP / ISO 100 gear oil generally provides weaker oil film strength than an owner manual spec'ed pre-2000 SAE 90 gear oils, offering lower wear protection to differential gears and bearings.
JMHO.
Note:A plowing/towing truck requires increased oil film strength against components wear protection.
Thank you for your patience ...
I would agree that this is fairly common for a high mileage 70s-era SBC engine. Seen lots that looked like this but continued to run for years.
this is not as bad as most of them i have seen but i get to see them when there is a problem
It looks like my cousins 70's pickup did at 300K+ miles. Nothing to worry about. Keep you the basic maintenance and it will be fine.
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