M30 "heat soak" phenomenon

[RockJock]

I’ve been noticing this phenomenon occur lately and I’m wondering if it could be indicative of a cooling system problem? As soon as I fire the car back up though, the temperature comes back down and the needle goes back to dead center. Has anybody here experienced the same thing?
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From Bruno’s site:

Why when I stop the engine and start it 5min after, the temperature needle is hitting the 3/4 mark?

• The phenomenon known as "heat soak" occurs when the engine is turned off. At this time, the combustion process is terminated. This terminates the momentum of the crankshaft, which in turn stops the turning of the water pump. As the coolant is no longer being circulated, the engine block and cylinder temperature increase for a period of approximately 3 to 10 minutes, depending on the engine design and additional components. During this time, the engine block radiates heat to the air surrounding the engine, which slowly cools the engine. However, the cooling process occurs slowly, and as a result, the temperature of the engine block transfers the heat to the coolant. The coolant temperature then increases, which in turn increases the pressure inside the coolant system. This is why the vehicle's coolant temperature gauge increases over a period of time after the engine has been turned off.

BMW E34 Website (http://www.bmwe34.net/E34main/Other/FAQ.htm)

[ArnZ!]

Yeah i have this only when ive been driving really spiritedly for a longish period of time, but normally i let the car idle for a bit before shutting it down to try an avoid heat soak, but it still kinda does it.

[BennyM]

Perhaps you could run a seperate switch and relay for the aux cooling fan to help with that. I know cars with hot enginges (like the Viper) automatically run cooling fans after shutdown.

[rob101]

Perhaps you could run a seperate switch and relay for the aux cooling fan to help with that. I know cars with hot enginges (like the Viper) automatically run cooling fans after shutdown.

Benny the other reason those cars run the fans after they shut down is because most more modern cars run electrical fans rather than fans off the crank/fan coupling I have had cars without "hot engines" run the fans after shut off. So the fans will be triggered by a temp sensor to turn on even after shutdown.

From a car perspective it is important to remember that the coolant temperature rising does not mean that the engine block temperature is rising in this case (in fact there is no additional heat going into the system at all when the engine is off it just transferring into a place where you can see it on the gauge (in the coolant around the temp sensor). So the question is, is there really a problem there?

[genphreak]

Rob!

Your baaaaaack!! We've been missing u dude!

'ssssupppp!! Didn't u move and get married n all that? Still got ur 525?

OP: The no start condition/backfire is nothing to do w 'heat soak'. The no start would be more to do with incorrect fueling at startup. The spark seldom fails- but poor spraying injectors, (A common fault is a dirty injector dripping fuel into a cylinder/intake once the engine is shut down. There is more than enough gas and heat to cause immediate detonation where you don't want it if re-starting when hot. Also check for dodgy fuel pressure (search for fuel purge / return valve stories - BMA sell the 'fix' kit for $10.00) and suspect the fuel Pump may be dying (they can go slowly or suddenly- sometimes, they can take years to go totally). TRE Performance Inc. - SPEC AFR Canton Corbeau RC Walbro 255LPH Fuel Pumps (http://www.treperformance.com) have great pumps for e34s, but need a little care and fabrication installing- inc. soldering. A full R&R kit is advisable if your time is valuable to you. Could also the water temp sensor the ECU reads near the thermostat (easy to measure using a multimeter) or possibly the Fuel Pressure Regulator on the fuel rail. If you don't know how close to spec they are; check air filter is clean, spark plugs are correct gap, sealing properly and not worn or fouled.

Enough to keep you busy there, unless you already know the answer to all those things as any self-respecting BMW owner does(n't).... LOL!

[RockJock]

Thanks for the input guys, it’s greatly appreciated.


OP: The no start condition/backfire is nothing to do w 'heat soak'.

The symptoms I was referring to are more along the lines described by ArnZ! but I don’t necessarily have to drive the car hard for it to exhibit this phenomenon (ambient temps 15-28 degrees C).


From a car perspective it is important to remember that the coolant temperature rising does not mean that the engine block temperature is rising in this case (in fact there is no additional heat going into the system at all when the engine is off it just transferring into a place where you can see it on the gauge (in the coolant around the temp sensor). So the question is, is there really a problem there?

To be honest, that’s what I was hoping someone would say. I’m just not sure why I didn’t notice it before, maybe I wasn’t paying as much attention. I’ve been told that WaterWetter (http://www.redlineoil.com/product.aspx?pid=74&pcid=10) helps. Maybe I’ll give it a shot.


OT: Just curious, for the guys down under; is the resource boom still going nuts or are you experiencing a bit of a slow down? With China applying the brakes it’ll be interesting to see if they can keep things under control (especially with problems mounting in the EU and US).

[genphreak]

Make sure you use the right coolant and the right mix, eg 1/3 to 2/3 coolant. The more water, less coolant in the mix, the better it transfers heat. I would not use anything not recommened by BMW myself, a lot of magic cures cause trouble. Exceptions to this for me are only a small number of modern gearbox/diff additives. With critical fluids like coolant it pays to stick with what the engineers think about their creation, rather than believing anything a 3rd party claims.

Resources are the place to be atm. Not even our banks can go wrong down here. Spot gold is over $1600 now, wh9ich just tells me that the world is feathering the nests of organised crime lords and greedy executives. It's insane. In Oz, we do okay cos everyone (and more recently Asia) needs coal and other resources, gold is not exactly plentiful here.

No slow down, but our manufacturers are having a hell of a time selling anything overseas with other currencies so devalued...