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///M3 Forum
The BMW E46 ///M3 is the M version E46 and puts out an amazing 333 HP and 262 lb-ft of torque at stock specs! There are an amazing amount of modifications for both the coupe and convertible models so read up and get started modifying your cars today!

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Old 12-17-2012, 02:43 AM   #1
DeclanM3
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Possible Thermostat Error

Hi guys,

Had some issues with coolant temps when I was on a drive yesterday. Coolant was fine all day then suddenly rose from the middle towards red in the course of a minute - 2 minutes tops. I pulled over as soon as it was safe at which point the coolant maxxed out at 114 according to the Intravee II which i believe grabs this from DME?

I waited for it to cool down then drove home with the heater on full. The coolant remained at 85/84 the whole way home for 55 minutes. Mind you I was driving very cautiously and had a max RPM of 2,800.. Not a very fun drive also considering it was 37 degrees outside.

My water pump hasn't made any noises and my coolant is still full so I don't think it's related to either of those things.

Could it be a case of the thermostat being stuck closed then when I restarted the car it reopened / the heater on full blast was enough to keep the coolant temp down?

Any ideas / things for me to test in order to diagnose the issue?

The fan is working fine and I was doing 60+ks an hour when the temp spike occurred.
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Old 12-17-2012, 12:12 PM   #2
DSilk56
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60 kph is less than 40 mph, which isn't very fast. I note this because the following things strike me:

1. The fact that turning the heat on full blast kept the engine temps down indicates that the water pump is circulating the coolant. The heater acts as a secondary radiator, which wouldn't do anything to cool the engine if the water wasn't circulating.

2. The fact that your car was overheating means that the radiator was not properly cooling your coolant; hence

3. Either your thermostat is faulty and either got stuck closed or isn't properly opening or your radiator/fan aren't properly cooling the radiator's contents.

This is where your speed comes into play. At higher speeds, the car doesn't rely on its cooling fan to pull air through the cooling vanes. The car's own forward motion does that. At lower speeds, and at idle, the fan becomes important. 40 mph should be enough speed to make the fan's contribution marginal, however.

Look at your thermostat first. If that doesn't cure the problem, look at your radiator's cooling vanes and water flow. If those are fine, look at your fan and fan clutch.

Last edited by DSilk56; 12-17-2012 at 12:14 PM.
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Old 12-17-2012, 07:56 PM   #3
DeclanM3
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Quote:
Originally Posted by DSilk56 View Post
60 kph is less than 40 mph, which isn't very fast. I note this because the following things strike me:

1. The fact that turning the heat on full blast kept the engine temps down indicates that the water pump is circulating the coolant. The heater acts as a secondary radiator, which wouldn't do anything to cool the engine if the water wasn't circulating.

2. The fact that your car was overheating means that the radiator was not properly cooling your coolant; hence

3. Either your thermostat is faulty and either got stuck closed or isn't properly opening or your radiator/fan aren't properly cooling the radiator's contents.

This is where your speed comes into play. At higher speeds, the car doesn't rely on its cooling fan to pull air through the cooling vanes. The car's own forward motion does that. At lower speeds, and at idle, the fan becomes important. 40 mph should be enough speed to make the fan's contribution marginal, however.

Look at your thermostat first. If that doesn't cure the problem, look at your radiator's cooling vanes and water flow. If those are fine, look at your fan and fan clutch.
Thanks heaps for the info. My speed was never below 60 and in fact was probably over 80 for a majority of the time.

I've ordered a new thermostat so I'll start with this then keep an eye on it and if I've got any more problems I'll look at the other stuff you've mentioned
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Old 12-18-2012, 12:43 AM   #4
illestminimike
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Had the same problem. Changed the thermostat and didn't make a difference. Check your fan clutch. Most likely you need a new radiator.
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