I just installed a new Atlantic British 4.6 long block in my 04 Disco due to the bearings went out in the bottom end of my old engine. My radiator is only about a year and a half old and my heater blows good heat so I don't believe my heater core is plugged. We also installed a new 180 LR gray t-stat. My clutch fan is also only about a year and a half old and appears to be functioning correctly. My auxiliary fan comes on at 210 as it said it should in the factory specs. The water pump is new. My issue is, as long as I am driving, the engine temp stays between 194 and 198. However if I have to idle it at a stop light, etc. for a short period of time the temps rise. The temp got in the high 220s. As soon as I move it drops right back down. Fluid levels stay constant and there is no sign of pressure in the line such as from a head gasket leak. Any ideas of what would cause this?

 

With all those new parts I doubt it's any of those. It's possible, but I think it's more likely to be air somewhere in the lines. Sounds like you need to try bleeding the system again.

 

Or the fan is blowing backward due to the belt being incorrectly routed.

I would imagine if you've done all that work you know the proper bleed procedure and belt routing, but those are the two most likely causes.

 

It seams to be ok with airflow, so belt routing or clutch fan. It appears the conders fan is working correctly

 

I'm going to try bleeding the system again and if that doesn't work I'll swap out the clutch fan. The belt is routed correctly.

 

Turned out to be an air pocket. I still think my 185 t stat is bad as engine sits at 195 down the highway and 208 at idle.