This may be of interest to those considering synthetics and synthetic
blends in older cars. I asked Quaker State about their use in my 78
Midget, and concerns I had about viscosity and seal compatibility.
This is an excerpt from the reply from their lubrication engineer.
(Q-State was very courteous and helpful, I might add):
"We would basically agree with you that the High
Performance 20W-50 would be a good choice for your vehicle. We do not
anticipate any seal compatibility problems using a synthetic blend.
We do hesitate to recommend our full synthetic in
vehicles older than 1980 which have the original seals.
The same would be true of your transmissions and
axles: we would recommend the synthetic blend over the full synthetic
if they still have the original
seals.
If you rebuild an engine, replacing the seals also,
you may use a full synthetic from the first drain. There is no
break-in period necessary on conventional oil. "
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