M42 Cooling System questions

[gusgriff]

I see a number of posts about cooling issues on the M42 and M44 engines. I need to separate fact from fiction. I have talked to a couple local people that said the M42 has a tendency to overheat. Another person said the engine cooling jacket design is less than optimum and opined that the M44 attempted to correct the faults. I have seem a number of posts on suggestions, mods and tips.

What is the real facts the M42 and M44 cooling system? what is the best maintenance steps and what mods, if any, give the most bang for the buck. I not believe throwing money after a problem is always the best solution.

An example is the $200-$300 Hi-Cap water pump. This is 4-6 times more than the stock pump. How much does it really increase GPM throughput. It may be worth it but the cooling jacket pressure drop increases with flow throughput. This pressure drop is close to being exponential I doubt it moves that much more water through the system. If the manufacturer says it moves twice as much they are quiet generous and if they say more you need to look at their test equipment.

The next hurtle is with increased flow is the radiator which is the same as with the engine cooling jacket. The pressure drop through the tubes/channels is added to the cooling jacking pressure drop. Bigger channels help the flow but not always the issue of heat transfer. You need as many heated water molecules as possible in contact with the channel metal/fins. I do not know now efficient the stock radiator is but if near max heat exchange with the stock water pump the Hi-Cap pump is not getting the help it needs to do the job. You need either more surface area of more airflow. If I am wrong please left me know.

[bazar01]

I bought a 96 ti with 174k miles and a blown head gasket due to overheat for less than $100. I had no idea what I had gotten into. After researching here and getting replies from knowledgeable members and other BMW forums, I have concluded that the cooling system on the M44 is sufficient and the only weak points are the plastic tubings that attach the rubber hoses to the block and head plus some other some plastic components in the cooling system like the reservoir in the radiator, etc.

Once I got the car back on the road after replacing the whole engine, coolant hoses, tubes and radiator, I noticed that the radiator fan hardly turns on unless you get stuck in the Atlanta traffic in the summer. The cooling system is pretty much sufficient but the plastic tubes need to be replaced every 100k miles to be safe.

Hopefully the more senior members will reply.

[teen ti]

bazar has pretty much got it, the only truly weak part in the cooling system, at least for the M44, is the plastic tubings

[gusgriff]

Thanks Fellows and sorry about the trirade about the Hi-Cap pump but I have a bug up my butt about companies selling something they claim is better. They hope you think if you paying 2+ times the price it is 2+ times better when it usually at most less than 25% better and they do not tell you what else you need..

[J!m]

A high-flow water pump (with metal impeller- very important! Stock plastic impeller pumps have been known to fail often. The impeller comes off the metal drive shaft) is never A bad idea.

So (lets say for argument's sake) the 'fancy' pump is only 25% higher flow; that is certainly better than stock flow, and is probably assuming a sterile flow path. If you have a 10% restriction in your flow path, your new stock pump is at -10% flow. With a +25% pump, you are at +15% with the same restriction.

Since I have worked in thermal spray for nearly 25 years now, I know the importance of cooling water to a plasma gun. You need either high flow rates or high surface area to reject heat. If you can't change one, change the other to get more capacity. Higher flow rate does have some value. But you can also increase area with a six cylinder radiator in your case.

Radiator should always be checked, and cleaned and/or replaced as needed.

Run only BMW coolant (the blue stuff) and distilled water. Tap water is your enemy! Its not much more than the green stuff and worth it.

Water Wetter from redline is not a bad idea, but not necessary if you keep on top of coolant changes and maintenance.

Also, most (if not all) M44 engines have a provision for an engine driven fan. If you are really paranoid about cooling, fit a six cylinder radiator, shroud and engine driven clutch fan in addition to the electric one and forget about it.

[gusgriff]

Thanks for the added info. I did not know about the BMW coolant and using distilled water. I already use wetter in my 535is and will use in the Ti.

With the engine being the M42 and assuming it cannot be modified like the M44, the 6 banger radiator and etc.make sense. I will check into this if it starts to overheat. I am not opposed to the Hi-Cap pump but need more data to get my mind around it.

When I pull the bad M42, the radiator will be cleaned. The replacement M42 engine will get flushed, new hoses, thermostat and pump. I got the one with the composite impeller. It is suppose to be an improvement over the plastic impeller.

[J!m]

If you stay on top of maintenance, you will be fine.

They did test the design in the hottest (and coldest) places on earth before going into full production after all...

[zoner]

The M42 cooling system has a little less plastic than the M44 - it doesn't have the plastic fitting in the rear of the cylinder head and the thermostat housing is aluminum instead of plastic - but it does still have the the plastic water neck in the side of the block, plastic radiator and reservoir, and plastic WP impeller (these are all parts that are subject to failure).

For the price of what you can get a new Behr radiator for, it's probably worth the peace of mind to go ahead and replace the radiator as well, assuming that the radiator is more than a few years old. There's a thread here on the forum that talks about all of the cooling system components and hoses and how to replace...

+1 on using the blue BMW coolant and ALWAYS distilled water- corrosion is probably the #1 killer of cooling systems and tap water is usually loaded with minerals that cause such corrosion.