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MECHANICALS With a 30 year-old automobile, there will always be discussion here - maintenance, modifications and mechanicals.

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  #1  
Old 13th February 2012, 03:25 PM
Lukas Lukas is offline
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Default Water Pump Flow Rate

Hi all,

I recently drained the cooling system of a 450, and was able to flush both the radiator and the engine with a garden hose. This is after disconnecting the top and bottom radiator hoses, then adding water in either direction at the top opening.

When I tried this with a 6.9, I couldn't flush the engine - presumably there was insufficient water pressure to get past the water pump, and/or the pump has a different design that blocks the flow when the pump isn't moving.

My back-yard-hack solution was to run the engine, let it pump the water out of itself, and constantly refill with clean water via the surge tank. This worked well, except that:

1) It sprayed rusty water everywhere: as the water comes out of the hose, dribbles onto the fan and get splattered everywhere. Extending the top hose with a spare section sorted that.

2) The pump only started working when the engine temp reached about 80 degrees C - assume it has some kind of thermal clutch? I had assumed it was direct drive. What's the benefit of such a setup?

3) When the pump was working, the flow rate struck me as not great - equivalent I suppose to about 2 teapots pouring at once (rusty, steaming brown tea). I worked it out as roughly being about 5L/min. Is that the normal flow rate, or is the pump worn?

Regardless of the above, it worked well and there is now nice clean coolant in there.

Ta

Lukas
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Old 13th February 2012, 08:17 PM
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Tony66_au Tony66_au is offline
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Default Re: Water Pump Flow Rate

So the engine had no coolant, only rusty water.

And its an iron block/alloy head combo with brass and copper components.

You couldnt flush the block from the top so you started and ran it sans intact cooling system.

First up, the thermostat will have been closed by the cold water hence the lack of flow thru the block.

Remove the thermostat and it will flow, even past the waterpump.

Secondly if you have sludge or goo you wont clear all the galleries with a garden hose.

Thirdly running an engine without an intact and full cooling system means that the cooling galleries in the heads wont have coolant in them, they will get very hot and cause issues. Even a few moments will cause some heat to soak into the heads which can damage them and hard bake any goo in the galleries.

Finally adding coolant to a system that has been without it for some time can soften hoses and gaskets causing coolant hoses to burst and possibly head gaskets to deteriorate.

Re this line 2) The pump only started working when the engine temp reached about 80 degrees C - assume it has some kind of thermal clutch? I had assumed it was direct drive. What's the benefit of such a setup? That'd be when the thermostat opened, and the temp guage will not have given you the temperature of the heads which may have been far far higher.

Hope this helps
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Old 13th February 2012, 08:41 PM
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Oversize Oversize is offline
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Default Re: Water Pump Flow Rate

I think you'll find it's the thermostat causing the problems. It'll block all flow through the top hose until it starts to open. It may not open much (if at all) when there's a constant flow of cold water coming in from your garden hose. There's actually quite a technique to flushing a cooling system properly and changing the coolant (post to follow)...
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Old 14th February 2012, 12:15 PM
Lukas Lukas is offline
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Default Re: Water Pump Flow Rate

Ah, the thermostat does that.

My method was the same as the first part of Mark's post, namely:

1) Disconnect top and bottom radiator hose
2) Flush radiator from both ends and via surge tank (try flushing engine, no dice)
3) Reconnect bottom hose
4) Refill system with water
5) Flush engine while it is running as per the above procedure

I always forget to do the heater hoses at coolant time.

The engine was full of water while running, save any air bubbles that might occur after the bottom of the engine is refilled via the radiator. There was plenty of gurgling going on, but I'm not sure if the air can get out the top with the thermostat closed. The water wasn't moving until the thermostat opened, but this is no different from a regular cold start?

Theoretical question then - what is the point of the thermostat? I.e., what's wrong with having maximum available cooling all the time? Don't cool engines run better than warm ones?

Also, why is there no thermostat effect on the 450?

PS - re going from no coolant to coolant: interesting that it can cause hose and gasket issues - is it thus better to keep running without coolant? I'm a fan of coolant mainly because of the corrosion inhibition properties, although in the case of the 6.9 improved heat dispersion is also a bonus.
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Old 14th February 2012, 02:52 PM
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Tony66_au Tony66_au is offline
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Default Re: Water Pump Flow Rate

Thermostats regulate the water flow as they are a smaller diameter than the radiator hoses and the back pressure they cause also helps the Pump impeller work better.

remove the thermostat and your car will run cold which can fool the cold start system to kick in (Cold start injector or choke will remain on) or in the case of an injected Benz the AAV will remain wide open causing a high idle situation and the flow on effects of this.

In a car with different metals in the cooling system such as the Mercedes which has Cast iron, Alloy, brass and copper id definitely run the Blue Benz coolant and i believe I wrote or contributed to a thread on this a while ago.

The OEM Coolant may or may not cause these issues and its mainly older hoses that suffer and silicone hoses are immune, as for head Gaskets?

If they are brass or metal then you have no issue but if they are composite (Asbestos or modern fibre) then you may have an issue.

But being an alloy head engine you MUST run coolant so all I can suggest is to make sure your system is clean, use OEM coolant and keep an eye on the hoses.
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Old 14th February 2012, 02:57 PM
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Tony66_au Tony66_au is offline
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Default Re: Water Pump Flow Rate

Re the 450 (M117) the thermostat may be missing, it may have been gutted (By which I mean someone removed it and then chopped the valve out and replaced what was left over) or it may be stuck open.

LPG fitted cars can also have extra bypass holes drilled in the base plate or the thermostat.

Basically bodgey shortcuts by tightarses to cure heating or cooling issues.

So id check that the 450 has a thermostat, Never run a car without one and if you must try for cooler or hotter engine temps find a thermostat that opens earlier or later (Different temp units).

Remember your AAV closes at 66 Celsius.

Above all else ignore any holden or ford "Tricks" to fix Euro cars because any short term benefit will bring long term pain.
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