[rrobson]

No, there isn’t. The oil temperature can happily spiral out of control while the engine and water temp remains low. Without an oil temp sensor you’ll not know either. The rad and fan will do a good job of keeping the water something like therefore keeping the engine cool. But without a substantial oil cooler it can be difficult to control oil temp once it begins climbing. All that will happen is you’ll lose oil viscosity and wave goodbye to your bearings. Oil pressure is as good an indication as temperature but again without a gauge you can’t monitor it.