My 89 Z24 2.8 has been running hot and normal lately and I am baffled what it might be. It will run between 200 and 227 and increase at a moderate rate under a hard load or stay about 204 under a steady cruise, though it will tend to creep up in the teens after a while too. I have been running the car in the winter and spring cooler months with the heater on and it ran a steady 195-200 according to the instrument gauge. Now that it is getting warmer out, so has the operating temperature. It ran a bit hotter for a while, then corrected the leaking fitting on top of the water neck.

I have used prestone quick flush, then switched to Prestone super cleaner which is operated 3-6 hours of driving in water before draining and flushing. This is the state I am currently in of driving the car with water and cleaner in the system. I have about another 4 hours of driving to do before I drain and flush the cooling system again. I was hoping this issue would have resolved itself with the swap of a new thermostat, though I think the other one was new too. I have replaced the thermostat with a 195 degree Fail Safe high flow thermostat, sanded the water neck flat so it would seal tight and replaced the weeping gasket on the metal tube coming out of the top of the water pump housing which runs over to heat the throttle body. I have new radiator hoses on the way and a new water pump to swap out once the super cleaner is flushed out, but I don't think those items and this super cleaner is going to make the car run a steady 200 degrees which my mechanic who had one said it should.

The cooling fan will come on at 225 degrees according to the snap on code scanner I am using to monitor the temperature for greater accuracy. It seems to show the instrument gauge to be pretty accurate. Any thoughts or ideas of what might be causing this or is this how these cars operate? I have only owned this one since September, so I have no idea how it should operate in the summer and heat and don't want any long cruising problems or junk the engine out of ignorance.

While I do not own a 2nd and flushing is good to do and all the new parts.I however may say it could be your radiator is just gooked up and no amount of radiator flush will remove that even lime away which I use want cut thru stuff like a issue as such.I suggest replacing the radiator just due to age and I would lay strong odds that will fix that temp range back to a normal use as it should be.I had a similar issue with my mazda but,not bad.I replaced my rad,heater core,plus wp and wow truck runs cooler,warms up faster and even in the high 90s no problem and I have a fan clutch not a electric like our js.I would just buy a new one from auto zone or advance or who ever you like best and do the change out when you drain the system to do the wp and be done with it.Keep in mind most radiators and heater cores want last 20 plus years with out eventually building up scale and unless removed and taken to be professionally done(waste of time and money) you can buy a new one for under 130.00 on a ball park cost.I would do this if it was my ride and well have on one already.

I know your right Ron and not ordering a new one would just bother me that I would think the thing could run cooler until I did order one......so I ordered a new one from Advance Auto hoping it will be here before the holiday weekend so I can install it at that time. I used the 15% off and get a $50 off coupon for ordering over $100 promotion, I also got free shipping too. The bill came to $126 which included tax. I hope the new radiator resolves my problem and the car runs as cool as I think it should all the time. I really want to put some long distance cruising miles on the car this summer with the top down.

I want to buy sway bar bushings, water pump and belt tensioner with the $50 off coupon when it comes which is why I opted for the Advance Auto radiator. Crossing my fingers I didn't just waste a bunch of bucks!

Good deal then.I know when my mazda truck had some mild gauge changes it was time to replace my radiator and this is actually very common on the b series trucks with the gauge going up then back down a touch.Saving money on those deals is the way to go and I use auto zone alot and every 20.00 I spend goes towards a bonus.Once you spend 20 five times you get a in store credit for 20 for free.I did my heater core too but my heat was ok,but just with it's age it was time to toss it and do it all at one time plus heater core hoses.

Resolved the fluctuating cooling issue with Prestone 6 hour driving super radiator cleaner, followed by a double flushing. Also replaced the thermostat, coolant, water pump, upper and lower radiator hoses, and of course....the radiator. $200 expense, but now I think she is ready for a summers worth of trouble free cruising far from home. Curbside cool down is just down time mamma wont stand for. The guy who has a small local junk yard told me on my last visit "You can't be cheap all your life" So I did him proud on this issue.

Great to here the issue resolved.

i know you said you fixed the issue, but just as insurance, check your burp tube make sure its clear. you should be able to take off the car and blow through it. i have a 91 RS 3.1 and i had major overheating problems. that tube was the cause of all of the problems. the car overheated so badly i had smoke from under the hood, prevous owner was a terrible mechainc. the temp gauge also wasnt working because he had the o2 sensor lead plugged into the temp gauge lead so the car had no 02 sensor signal, it took me a while to figure that one out.. i could not figure out why that car ran so badly. its been running like a dream for 8,000 miles since all of that was fixed. anyways check that tube, it goes from the top of the thermostat housing to the overflow tank.