I worry about my FL overheating - probably needlessly. I normally run my K series 1.8 with an engine oil cooler running from a thermostat take off plate. That’s an extra but you screw onto the filter mount, it opens at 95ºC. I recently had an oil line to that cooler split and dumped a lot of oil on the road. Wasn’t a happy chappy!

Anyway I decided as it is winter here too disconnect and remove the oil cooler’s take off assembly and blank off the pipes to the cooler itself. I’ll reorganise/ reroute the oil coolers plumbing and use braided lines and fittings to match to avoid another catastrophic oil line failure.

Now I’ve noticed that the oil pressure runs higher. I hadn’t considered that the oil cooler would lower the oil pressure.

My questions are: Should I consider changing the grade of oil I use to a thinner oil in the winter months. Temps are in the single digits here and we regularly see hard frosts -7ºC… so the running is much cooler than in summer. Temp’s then range in the mid teens to low 30s. I normally run Castrol Magnatec 10W / 40. Should I consider a 5W / 40 or a 10W / 30? Will a change of oil grade help to raise the oil pressure - should I even be worried about this at all?

The oil temp with the cooler disconnected sits around 95 to 100ºC whereas in the winter with the cooler connected it’s rare to see it over 90ºC.

An oil cooler can and often does drop the oil pressure seen at the main oil gallery. It should only be a few PSI so is generally of no significance. I personally prefer oil to water coolers as it means the oil can't be over cooled in winter.
On a road going K series, the oil cooler is not really necessary, unless regular heavy towing is being done.

Oil grade is important and should be strictly adhered to. A 5w30 is too thin for the K series, which was designed before that grade became popular.

A 10w40 semi-synthetic is fine for all operating temperatures between -20°C and + 30°C. You can make it crank a bit faster when very cold by using a 5w40 fully-synthetic oil instead. A 5w40 fully-synthetic will also provide better lubrication at high engine temps too.

I'm a big fan of 5w/40 engine oils. I'd make me chips in it if I could.