M13A engine Overheating

Hi All

Sorry for the delayed update on my over heating problem and thank you for the various suggestions as to resolve it.

I had a number of well meaning but depressing opinions that I had a head gasket leak, but after 45 years in heavy road transport engineering I remained doggedly convinced it was a coolant circulation issue. Fordem's input was very interesting as I had never considered Jimny M13a engine as having the thermostat down stream of the radiator. Stupid ! As I had already replaced the dam thing.

Using an IR thermometer I checked (given its limitations of measuring external surface temp), locations around the circuit the heater matrix ports had a 7 degree drop suggesting there was a through put and by far the hotspot was the thermostat housing at 89 degrees.The pump impeller was doing its thing, radiator flow was fine and I had replaced the thermostat, what the hell ! The prophets of doom had to be right it was a head gasket.

One more go before I take the lid off. Why oh why do designers not put service items easy to get at, new thermostat out again and in a pan of water. According to the kitchen temp probe its opening at 96 degrees ! I had blindly believed that my new replaced would have passed QC and all was fine to fit.In with another new one (having checked), lo and behold little Jimny is singing like a big Volvo FH on song all is well again.

Cheap pattern parts, if that's what this was, don't necessarly do what it says on the label (or stamping).  I once bought an oil filter for a Nissan, gave the parts shop the VIN and everything.  Started the engine and the rubber O-ring blew, dumping all the fresh oil onto the garage floor in 5 seconds flat.  It was completely the wrong size.