Temp Gauge

Hi, I have a 1988 740 Turbo with, 2.5 catback, cone with heatshield, NGK plugs, manual boost controller, E. Fan and no A/C. My problem is i just installed a new 3 Row Radiator, shortly after i blew the lower radiator hose, which was replaced and i filled the radiator up with water/coolant.
I was driving the car today and i noticed the temp gauge was 3/4 of the way towards the red, stays there for about 5 minutes and goes back to the middle. the car has never done that before, even with the old radiator. What could possible cause this? I dont know the exact mixture of coolant/water is in it. I was thinking about emptying the system and bleeding the air out, and put a better mixture in it. The car did over heat and cut off when the hose blew and i am worried about a messed up head gasket, but i hope not .

Any suggestions?

mine did this....and here is what i learned.....1st...the guage going up, is your water getting hotter...poss due to coolant loss (are uou sure you are up to "fill" w/the coolant).....then...when the guage goes back down...it is possible...the hot water is no longer surronding the heat sensor...and it is exposed to the air...giving you a reading of the air temp outside the heat sensor...not the water temp....as there is no more water around the sensor...it may have drained out...lesson...just cause the water temp guage read hot...then back to normal...all may not be well...be careful!!..i almost runined my 940 cause i fig the temp was ok...and did some driving w/very little coolant in the system....dbl check for leaks & make sure the resovior is up to the proper mark.....

THe last time i filled it up to the fill line, and turned the car off, coolant came back up to the tank and it was filled to the cap with coolant. I dont want it to over fill or anything like that, so I will add a little more coolant and see what it does till i can have it tested

yea...just make sure you can see some coolant in the plastic bottle....it should be under some pressure when hot...but, if it is leaking out of the top...you have a pressure leak at the cap, or o ring around the cap or something...when i am running my 940 hard...and get it all "hot and bothered" ...if i remove the cap to add some coolant...i hear a big woshing sound as the system becomes un pressurized.....

When i remove my cap when its hot it starts to splash about and the coolant rises up as if it wants to over flow

yea...give it a few min to calm down.....sounds like your ok...as long as you are not leaking or loosing coolant....(like i am around my wter pump...slowwwww leak).....waiting for my cam so i can do water pump, cam, timing belt & front oil seals...

If my coolant starts disappearing again, i am gonna check to see if the headgaset is still good, and check to see if theres coolant in the oil