SAE 30 Oil and Operating Temperatures

[Tham]

The general tendency for most cars in Malaysia
is to use a multigrade engine oil, with typical
SAE ratings of 20W-50 and 15W-40 for the normal
mineral-based ones, 10W-30 for semisynthetics
and down to 5W-30 for the full synthetics.
Multigrades are relatively expensive.

Pennzoil currently has a single grade "heavy duty"
SAE 30 mineral oil marketed more for diesel engines
over here, with an API rating of CD/SF. They call it
"HDX 30". (An SAE 30 oil by Pennzoil, of a different
name marketed more for petrol engines then, was
actually filled as stock in engines of new Toyota
Corolla AE80s with 2A or 4A engines coming out from
the factory here in 1984 or so.)

I was wondering if it was alright to use this long
term in my old KE70's 4K ? Ambient temperatures
here have grown much hotter over the past twenty
years, partly due to global warming here I think,
and 38 degrees celsius in the daytime is common.

I tried using it a few times, and the tappets and
timing chain seemed extremely noisy on a hot
afternoon. I'm not sure if engine wear would be
higher in long traffic jams on a hot day.