Water Pump Flow Rate

[Lukas]

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

 

[Tony66_au]

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

 

[Oversize]

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)...

 

[Lukas]

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.

 

[Tony66_au]

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.

 

[Tony66_au]

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.

 

[Tony66_au]

While im at it, Water "Pumps' in Cars are impeller pumps so they scoop and push the fluid similar to running around a kiddy pool to make a vortex.

A lot of people mistake impeller pumps with other types and expect big things from them but what you get is long life, minimal moving parts and the cooling job done.

they usually die after time and commonly #### the bearing and shaft seal leaking coolant but on cars left a while and without coolant can suffer from the impeller vanes (that move the water) actually rusting away.

So its all good from the outside, but rusted away on the inside.

 

[Oversize]

The thermostat regulates coolant flow and only allows recirculation within the block when the engine is cold. This speeds up the warm-up phase, thereby limiting emissions, engine wear and fuel consumption. Once the engine is warm, the thermostat opens and allows coolant to flow through the radiator.

Engine's have an optimum operating temperature and if it's too cold the rings will wear out quickly, fuel won't atomize sufficiently and tends to pool, plugs will foul, it will run rough and use more fuel. It's even possible excess fuel will make it's way into the sump and dilute the oil, which could cause excessive bearing wear. An engine that's running too cold engine is like only driving to the local milkbar every day. Terrible for engine wear. You may've heard the question, "Why do taxi engines last so long"? Basically they never cool down!!! I've always thought that if you had a heating element in the sump which was running when the engine was off, it would just about last forever.... That's assuming it's maintained at appropriate intervals with the usual consumables.

There's usually at least one small hole in the top of the thermostat (with a one way valve), which allows any trapped air to bleed out of the block and eventually into the expansion tank. I remember drilling additional holes into some thermostats (adjacent to the one way valve) as a remedy for air pockets etc, which was a factory endorsed modification! Remember for the one-way valve to effectively bleed trapped air it must be positioned at the highest point within the housing. Basically rotate the thermostat (cover off) until the small hole is at the highest possible point.

Yes, replacing coolant may cause leaks that weren't there before. It cleans and inhibits further corrosion and will find the weakest link in the system. However once these leaks are rectified, you should have trouble free motoring. I've never heard of coolant destroying gaskets and it's more likely the mating surfaces weren't flat, or torqued down correctly. Coolant will also increase the boiling point significantly and stop your car overheating in the Australian heat. And stop it freezing in the high country.

The alternative is to just run water, which will go rusty pretty quickly. That's the insides of your engine and cooling system corroding away! It make take a while, but things will eventually fail in a big way. Radiators, waterpumps, thermostat housings, alloy hose connectors, cylinder heads and the dreaded heater core. On an old Benz owned by someone with limited funds and little knowledge or skill, this fault alone can be enough for them to walk away. The moral is always use a suitable coolant in anything that is liquid cooled.

 

[Oversize]

Tony I thought gycol (coolant) was derived through organic means and being water soluable, it'd be ok for the sewer. If not I'll certainly be changing my procedures in the future. Coolant won't mix with oil and stay in suspension; they will separate if left to settle. However is that because coolant contains water? Is it possible to mix oil and non-diluted gycol?? Still more to learn... sigh!

 

[Tony66_au]

All hydrocarbons are natural mate, decomposed cellulose fibre from plants and trees turn into crude oil for most but ethylene glycol is also known as wood alcohol.

Many solvents are also water soluble like metho and Ethanol which is derived from corn or sugar cane.

I actually have a mate (Dad of one of my daughters friends) who works for the EPA and will ask him about the specifics.

For what its worth I used to recycle my sump oil by adding turps and spraying my fences with it back when paling fences were made with hardwood instead of this awful pine they now use, I also use it to start bonfires (I can burn off if I want to )

But the EPA guy that came to check the workshop stated that I had to add it to the waste oil collection and even plain rusty water. As for the oil collection mob? Well I added a fair bit of Yoplait (Its French for blown head gasket) oil n water goo to the tank as well and they never said boo.

I reckon small amounts youd be fine with but if a commercial place did it they'd end up out of pocket in a big way.

 

[BenzBoy]

The best way to dispose of sump oil is to pour it on a meat ants' nest. Mind you, I've heard of some pretty big meat ants of late so maybe they are genetically modified...
Regards,
Brian

 

[abl567]

The best way to dispose of sump oil is to pour it on a meat ants' nest. Mind you, I've heard of some pretty big meat ants of late so maybe they are genetically modified...
Regards,
Brian

they would certainly be friction modified

 

[WGB]

So - having fixed all the eco problems - what really is the expected flow rate from a water pump.

I would have expected a significant gusher unless the pump or impellor was corroded or obstructed.

Bill

 

[Tony66_au]

Bill its a how long is a piece of string question really.

But they are restricted by the Thermostat.

Im not sure about Mercedes but the flow is determined by how many vanes (Or blades) and things like anti cavitation discs as well as their condition etc.

I wouldn't think they are volumetrically efficient either as they are not a tight fit in the housing and there can be a substantial gap between the impeller and the front of the block which makes up the second part of the housing.

How do I know this?

Because I have in the past used electric water pumps on performance cars and struck problems because the flow rate was too high amongst other things.

An average V8 engine water pump flows between 20 Gallons per min and 40 GPM, Electric units can flow as much as 80 GPM and Ive had a play with these units fitted with a variable flow adjustment.

And at the end of the day the variable unit worked best at around 35 to 40 GPM.

I'll expand on this when I get back in a few hours.

 

[Lukas]

Interesting points all, ta. The 6.9s flow rate was roughly 1.3 Gallons / minute.

The thermostat was likely only just open given the constant addition of cold water. Still, that seems low. Will add it to the long list of things to "look into", or might check another car.

 

[Tony66_au]

Interesting points all, ta. The 6.9s flow rate was roughly 1.3 Gallons / minute.

The thermostat was likely only just open given the constant addition of cold water. Still, that seems low. Will add it to the long list of things to "look into", or might check another car.

1.3 GPM equates to 5.8 lt per min so thats not right, Id assume that the cooling system holds between 12 and 25 lt of coolant (An exact figure helps BTW) and you would circulate at least this amount per minute assuming an Gallon = 4.5 lt.

In reality this figure has to be measured under moderate load (Engine) with the temp at 80 degree's Celsius and the thermostat wide open.

There are numerous variables that also need to be taken into account such as coolant viscosity and state of the cooling system but at a guess id say your system would have to circulate 5 to 8 times per minute to hold a good operating temp.

Too cool and the mixture gets richer which leads to all sorts of issues and too hot also leads to issues.

When we were doing the setup on a particular car it had an all alloy block and race heads and we ended up with a thermal scope (Infra red video scanner) to measure cooling performance in various areas of the engine.

For example you would point the device at the heads looking for hot spots and if the flow was too fast as it would circulate through the radiator too fast to shed heat thru the system.

We did this on a borrowed chassis dyno to simulate engine load with 2 large fans to create a cool airflow, we also at one stage had 3 jetflow air heaters blasting the front of the car creating up to 60 degree air temp through the radiator and the whole time the Dyno would take readings.

The findings were astonishing.

As to why this was being done?

A clients desire to run the Cannonball run in the Northern territory, More money than sense lol and a nice GM product to play with although it showed numerous flaws even for day to day Summer running.

Personally?

Id drop a good radiator into the car with issues, a new water pump, a brand new thermostat and radiator cap and start with that.

Thermostats come in different temperatures and some open at far lower temps and id go with a lower temp although if you want nice hot heater temps id swap it out with a high temp open thermostat for those freezing ACT winters.

Oh and have a sniff of the old Rad cap and see if it smells like exhaust gas.

 

[Tony66_au]

By the way, Im not a qualified Mechanic Lukas.

But I used to employ them, get my hands dirty every day and I was the "Guy who thought outside the box" when they got stuck on stuff.

This often was something simple that had been overlooked, or something really weird and oddball (Not unlike me) that they may or may not have found after eliminating everything else.

Plus as an enthusiast I was always finding new and interesting parts, aftermarket stuff and diag toys (Like the thermal imaging gear)

 

[Oversize]

I'd replace the thermostat first and see if the flow rate improves. Then I'd look at the radiator and finally the water pump. If it's been running rusty water for a while, there's a fair chance there'll be more than one problem...

 

[Lukas]

Thanks all - I need to get all 3 cars up to the same level in terms of routine stuff, so will drop the coolant in the others and see what flow rate they show. I agree though that it seems low and will likely need attention.

Another numpty question comnig up shortly.....

 

[Tony66_au]

The only Numpty question Lukas, is the one you don't ask mate.