Temp gauge question

[s13redmon]

Ok, i just swapped a ka24de into my 1990 240 and it's reading high on the temp gauge but it doesn't seem like its actually running hot. I can let it sit and idle and it will stay at about 2.5 lines on the temp gauge but when i take it out and drive it shoots almost up to hot and the higher i rev it, the faster/ higher the gauge goes. I didn't put in a ka24e temp sensor so i'm wondering exactly how much of a difference that would make as far as the gauge reading. Also, with the heat on full blast the air coming out isn't that warm, even when the gauge is on the last line before hot, so I'm wondering if the thermostat (brand new) could be the problem.

[biggie]

Sounds like air in the coolant system, need to bleed it better. And yes it is actually overheating, don't drive it until you've fixed it.

[breadbox]

Put Car up on ramps so that the rad is the highest point in the car. I just replaced mine last night, I had similar symptoms except my heater blows hot when it supposed to. Make sure the thermostat has that jiggle valve and its at 12 o clock.

My gauge was reading weird, bleed the system again. If you have air/low coolant in res it seems to start sucking the upper hose closed. so add coolant to over flow and bounce the car a ton. and make sure no air pockets are trapped. I jumped on the front of my car for like 5mins. while squeezing the upper rad hose every once in a while. it still reads a little high but after I took it off and cleaned the connection it read the temp better and it didn't fluctuate with rpm.