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1995 W140 S280
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49 Posts
Discussion Starter #1 (Edited)
Hi gents,

Might be a dumb question but here goes anyway; so you know how some modern cars keep the fan (and water pump?) running for a bit after you shut down to cool it and counter the effects of heat soak? Well, a 140 obviously doesn't do that given it's age.

I was wondering if it's a complete waste of time and money to install a little turbo timer that you see on boosted cars where the pumps and fan or the entire engine continues to run for a bit after you've removed the keys and left the car.

Currently, if feasible like when parking at home, I leave it in accessory for a few minutes after shutting off and the fan will continue to run, but I'm not sure if it's helping much as the water/oil pumps aren't going.

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While we're on the topic of "possibly overkill measures in engine care", has anyone ever heard of priming a gasoline engine after it's sat for a while to reduce the startup wear and if so, how do you go about this?

Thanks in advance and have a good weekend everyone.
 

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2002 Mercedes ML320, Mercedes 190E 2.3L (sold), 2001 Mercedes c320(gone)
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1,391 Posts
Hmmmm, very interesting. What about the battery? Can the battery handle the fan for a while? I know even while doing ECU programming DAS strongly recommends connecting charger as the fan will be switched on during the process. I can imagine the more recent fans will be a lot more energy efficient and may be more practical. Will you also consider changing the fan to something with lower power draw? Sounds really interesting.

A second battery may be good to add with those dual battery relays so your starting battery has no problems.


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1994 S600 Coupe, 1995 S600 Coupe
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1,712 Posts
At least on the S600s, the pump in the duovalve runs for awhile after shutoff, circulating coolant on hot days. I suspect other models do the same.

Jon
 

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600 coupe, one of the very first built
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52 Posts
Currently, if feasible like when parking at home, I leave it in accessory for a few minutes after shutting off and the fan will continue to run, but I'm not sure if it's helping much as the water/oil pumps aren't going.
I come from the Jaguar V12 world, where engine cooling is the king. The majority of those V12 engines in the Jaguar lineup from the 70s and 80s suffer badly from what they typically call "heat soak" after shut down. A lot of people recommend the Craig Davies electric pumps, installed in the lower radiator hose.


They can be wired to run for a 2-3 minutes post shut down. A good battery can handle the load. Just the fans, w/o coolant circulation does almost nothing to help with spike in the temperature, especially in the back of the block/heads.
 

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1999 S500; W140.051
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694 Posts
Duovalve does not move enough water to be meaningful at mitigating post shutoff heat soak.

As stated previously, moving air alone doesn't do much to mitigate heat soak AND moving air is energy consumptive. Measure or look at current specs on the electric fans. Those twin fans on the W140 running full will draw 20A or more I'm sure. Moving water with a pump doesn't take so much energy.

Not many 'modern' car mfrs have decided to add the complexity of electric water pumps to the design. BMW does this on some models and they use it as the only water pump on at least some water pumps.

I have used the Davies-Craig pump in config to pump cool water to the back of the cylinder head on an old '72 MB 2.8 liter straight six (I-6) with alum head on iron block. That config is the worst for this issue and anyone with experience on those cars knows that after about 80k miles needing a head gasket job is to be anticipated any time after that point.

4-cyl designs even with alum head on iron block are not nearly so problematic. With modern open-deck aluminum block designs with aluminum head, head gaskets can be very long lived; even more than 200k miles.

I owned several open-deck I-6 engine Volvo cars and seen them go 240k before needing head gasket. M120 is a 'twin' I-6 motor in V config. It might go a long time on a head gasket, but I don't have direct experience with those cars.
 

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600 coupe, one of the very first built
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With modern open-deck aluminum block designs with aluminum head, head gaskets can be very long lived
My understanding following the Jaguar community is that head gasket is almost never the issue with post-shutdown heat soak. They are overly-worried about the valve seats - apparently if you drive the car in, shall we say more spirited way, and then shut the engine down, within 1-2 minutes, coolant temperature in the heads can exceed 120-130°C.
The Jaguars have a less-than-typical expansion tank, which is not at the highest point and bleeding the air in the coolant system is far from easy.
In the even one has air bubbles and coolant that is close to boil, bare metal surfaces exposed to heat = NOT good.

I don't know if any of this applies to the M104, M119 or M120 engines.
Cooked plastic/rubber in the engine bay is certainly a concern though.
 

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1995 Mercedes S420, 2000 Land Rover Discovery II, 1985 Lotus Turbo Esprit
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1,643 Posts
I'd have to think that the engineers thought of all this when they designed the engine and cooling system for these cars. If post-shutoff heat soak were a serious issue for these motors, I feel like we'd all know about it by now.
 

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S 350 Turbo diesel,Porsche 944 (83,84,85 and 86),Toyota Supra MA61 85,Opel GT 71
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156 Posts
Porsche 944 and 944Turbo always keep the fans on (turbo also has a electric pump) after you shut down the engine to cool it if the day is hot and engine temp is higher.And they use 55/60Ah batteries and no problems with the battery discharging.Sometimes the fans are on for 5/7 minutes.So there should not be any problem with battery discharge in the W140 because it has a 100Ah battery
 
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