Switched from 10/40 to 20/50 and car runs hotter.

[J.HK]

I switched from 10/40 winter oil to 20/50 summer oil today and my car runs hotter. It was running at 180, now it runs at 210. This makes no sense to me.

Thoughts???

[stormcrow]

The heavier oil could be putting more of a load on the engine. I know when I switched from 20 W 50 to 10 W 40, my mpg went from 20 to 23/24 mpg. So, it definitely does have an effect on the engine.

Steve