i had a hilux work ute on a minesite years ago. it only ran up and down from the workshop to the pit so it never had any decent runs at op temp. a couple of times when i changed the oil i could hold the oil filter upside down with no oil coming out it would sludge up so bad.
we would idle it on a mix of diesel and oil for 20 minutes then drop that and put new filter and fresh oil in. off it would go for another few weeks.