No the mention of the viscosity difference was not exactly an oil related thread type of response. If you are establishing new wear patterns in there it may increase heating.

The thrust loads or general loading a diesel presents are heavier and the block, crank etc are designed to deal with it. They still require more strength of cuishioning than a gas cars viscosity to keep the parts separated. You basically have a gas cars oil viscosity at the moment.

Thats especially why heavier grades of viscosity are recommended for the older diesels compared to gas engines. You do not lose much if anything financially by replacement with the correct thick enough viscosity lubricant.

Remember I mentioned to save the present oil. If the higher viscosity oil lowers the temperature fine. All things considered it should restore your oil pressure at idle. If not then you still have the present oil to use later.

The lower oil pressure at idle now indicates the current oil is far thinner than what was present before. I am not going to look at my manual but 10w-30 is only good up to a very low ambient temperature in these engines. 5-30 only usable at constantly under under zero perhaps. Talk to the guy that is helping you with the injector area leak.

If he really knows what he is doing he should have an answer one way or another for you. This is not a discussion about the respective merits of synthetic or normal oils, brands to use etc. Those are really the basis of the true oil threads.

Last but not least it is your engine. Why even risk the possibility even if it is an outside one? Read your owners manual. If it allows it fine. If not and you continue to use it there may be issues currently and very expensive ones down the road.