E21 Overheating Help

[jacksone21]

Up until about 3 weeks ago my E21 has been running before 1/2 on the temp gauge. However it seems to be getting up to 3/4 almost every drive, out of nowhere. Before, I had replaced the thermostat for a 71 degree one and that fixed my previous overheating issues. I am thinking it could be a temp gauge issue itself because the gauge goes up when I rev it a bit in neutral. Apart from that, it’s can be jumpy at random times when I’m driving. Also when I stop, the top two hoses on the radiator are much hotter than the bottom one, if that means anything. Currently working on a radiator flush in case it could be that but I’m leaning more towards a temp gauge issue. Any ideas or help as to how to fix or diagnose this issue? Thanks!

[alsimma95]

If the top two hoses are hot while the bottom one (connecting thermostat to rad) isn't, that usually means the thermostat isn't opening up.. Did you make sure to bleed everything well? I had a little overheating issue that turned out to be an air bubble in the cooling system that resulted in thermostat not opening up.. Besides the obvious there could be some grounding/wiring issues, lots of info if you do a quick google search. GDAus has a pretty comprehensive answer for these electrical issues here, https://www.bimmerforums.com/forum/s...0#post29622430 post #18

[jacksone21]

So I cleaned up all of the wiring behind the temp gauge and then my car was running at about 1/4 at idle. After a couple minutes of driving it shot straight to 1/2 and then to 3/4 after another 15 seconds. Is there something i’m missing here? After stopping the car it went back down to 1/2 and then upon turning it off it stopped in the red, the wrong side of the gauge. I have verified that the top two hoses only get to about 170-180 f on the hottest days and the lower rad hose is usually about 30-40 degrees cooler. Do I have to redo all of the wiring? This is just confusing me and I don’t really know where to go. Any help or guidance in the right direction would be appreciated thank you

[320iAman]

What thermostat are you using ? Probably 80C one--stock , Here is 71C one opens up faster delays heating up--I use 71C one., also in hot weather 75/25 is best, 75 water 25 coolant,, water cools down faster than coolant. winter,fall,spring- 50/50 works.

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Randy

[mxl556]

Of course, it can be air in the system, but since you have measured the temperature at the hoses, it sounds like a gauge malfunction.
Sounds like wiring to the gauge, can also be a instrument cluster itself. If you have not done it, I'd check the connection at the sensor under the hood. It sounds like you checked the cluster connection/ground nut? Also it can be an instrument cluster/gauge itself. Printed circuit board may have broken connections.

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by the way lower temp (71C/75C) thermostats would not fix overheating issues. Cooling system and its capacity is designed to maintain 80C. Putting the lower temp thermostat would just make it run cold on the highway or when the cooling system is operating below its max. capacity and would not provide any benefit.

[320iAman]

I doubt an air bubble is the issue, I said a dozen times before, these are very small radiators, thermostat opening earlier will definitely drop temperature 80 C is 176 F--thats were the thermostat opens and you get full circulation excluding the heater core until then the circulation is not going thru the radiator limited to the engine block and parts attached to it. 71 C is 159.8 F and so the thermostat opens for full circulation 17 F sooner, the heat will not come down from 80C unless ambient temperature is fairly cool, adding water wetter will bring the temperature down a few more degrees, yet if your driving 90F plus expect the temperature to be in between 1/2 and 3/4 marks,, these cars run at the 1/2 mark typically,, want the temperature down get an aluminum radiator with 1 in tubes. I got tired of my temp gauge being at 1/2 to 3/4 due to summer heat, so I installed an aluminum radiator now on the freeway at 65 mph and 90F plus- the temp gauge is in between 1/4 and 1/2 and closer to the 1/4 mark---the difference is aluminum and its larger takes 3 gallons of coolant. So the best that can be done with the smaller oem radiators when it heats up a lot is to use 75/25 water to coolant- 71C thermostat and make sure your radiator is cleaned up inside and outside-inside by some citric acid cleaner and out side the louvers dont have a lot of bugs in them and debris.

Randy

[alsimma95]

So is it an overheating issue or a gauge issue? When he said he verified the top hoses only get to 180, is that when the gauge is measuring over the half mark? My car idles between 1/4 and 1/2 and usually reads ~180 with a temp gun, 200 at 1/2.. Will get heat soak that causes it to rise after I shut it off or idle too long, but always goes down while driving...

Need to verify its actually overheating when the gauge is reading high, then can decide to tackle the overheating or the electrical issue accordingly. Randy has some solid advice for getting it to run cooler, but if its just an erratic or faulty gauge it wont matter how cool the thing is running

[jacksone21]

Turned out to be a gauge and connection issue! After making sure the connection was good after removing the cluster, the alternator was having issues. Or so i thought. That was causing the gauge to be jumpy and I just had to take apart the cluster again and straighten and clean everything out one last time. That seems to be a fix, running steady at 1/2, where it should be in this California heat. Thank you everyone for your help!