Help with hot running m88

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85MSteinway
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Help with hot running m88

Post by 85MSteinway »

Symptoms: runs hot in traffic, even in the current mild conditions, in fact the ambient temperature seems to have no bearing on engine temperature. When the car is moving it is cool. I'd say the exact opposite (far to left side of midline) of when idling in traffic.

This is what the temp looks like when idling in my garage:
Image

This is what the temp looks like if I bring RPM up to 2k. Vehicle is not moving, just sitting in garage with a little bit of pressure on accelerator. 90 seconds later temp drops to mid point (acceptable for me).
Image

History:
I replaced coolant. PO was running green stuff, I replaced with zerex g48. Symptoms are the same.
I replaced thermostat with BMW part provided by ecstuning.com. (part even said "made in W. Germany") Symptoms are the same.
I replaced viscous fan clutch with Mahle-Behr. Old clutch was a little loose. New is much tighter. doing the newspaper test suggested by others resulted in shredded newspaper. Symptoms are the same.
After doing some fan belt replacements on my wife's L6 I noticed the M6 did not have a fan cowl like the L6 does. Probably should have noticed this a long time ago. installed new cowl. Symptoms are the same at idle, but temps drop quickly to the left side of mid and much further to the left side of mid once car is moving. No history on why previous owner(s) removed cowl and did not replace.

My thinking is next step is water pump replacement. I believe it to be original with a little more than 90k miles.

If anyone can suggest anything else or a way to test the pump before replacing the pump, I'd be very appreciative. Anything I should do or lookout for if pump replacement seems like the next obvious step?

Thanks!

Jay
L6
85 M635
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Brucey
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Re: Help with hot running m88

Post by Brucey »

If you have not done so before now, I'd check the radiator is flowing water well enough and isn't partially clogged.

cheers
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Da_Hose
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Re: Help with hot running m88

Post by Da_Hose »

Definitely check for coolant flow, but if spooling it up cools it down, I suspect your fan mechanical fan clutch, or electric fan. I think it more likely that its your electric fan that is the issue, and sounds like you already addressed the mechanical fan clutch.

The electric fan is meant to make a difference at a standstill or very low speeds. Once moving, the wind blowing into the radiator is more than the fan can generate. I would jump 12V to the electric fan and verify it runs strong. Then use an IR thermometer to verify it is kicking in at running temps.

Jose
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sansouci
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Re: Help with hot running m88

Post by sansouci »

Sort of a question for you cooling experts: When does the A/C pusher fan come on? Is it only powered when the A/C is running or is it only thermostatically controlled? How does the temp at idle respond if you have the A/C on?
Jose is on the right track.
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baders
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Re: Help with hot running m88

Post by baders »

The auxiliary fan is on when;

1) Coolant temperature normal speed switch (91 C) is closed or;
2) Coolant temperature high speed switch (99 C) is closed or;
3) A/C evaporator temperature regulator energises the K1 normal speed relay.
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Pod
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Re: Help with hot running m88

Post by Pod »

You could try changing the temperature sending unit with a known-good one to be sure that the gauge is reading true.
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86_6series
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Re: Help with hot running m88

Post by 86_6series »

I have to say that you can't figure out the problem when you don't know where it is.

Buy one of these and it will tell you what the temp difference is in the system.

Upper hose temp vs lower hose temp vs heater valve hose before and after then
radiator temp upper to lower. Thermostat housing vs water pump temp etc.


https://www.amazon.com/Etekcity-Lasergr ... 186&sr=8-3
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85MSteinway
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Re: Help with hot running m88

Post by 85MSteinway »

Brucey wrote: Mon Dec 23, 2019 8:40 pm If you have not done so before now, I'd check the radiator is flowing water well enough and isn't partially clogged.

cheers
What would be the best way to test flow?
Pod wrote: Thu Dec 26, 2019 9:00 am You could try changing the temperature sending unit with a known-good one to be sure that the gauge is reading true.
Yep. not a bad idea. I'll probably do that.
Da_Hose wrote: Tue Dec 24, 2019 9:22 pm I think it more likely that its your electric fan that is the issue, and sounds like you already addressed the mechanical fan clutch.

Jose
Mine comes on when A/C is engaged. but not when it gets hot. when the AC is on it doesn't help. I'll try jumping 12v and keeping it on to see what happens. Seems to run strong but loud. Perhaps this will be my first move. A fan replacement and figure out why it isn't coming on when hot.
86_6series wrote: Fri Dec 27, 2019 5:09 pm I have to say that you can't figure out the problem when you don't know where it is.

Buy one of these and it will tell you what the temp difference is in the system.

Upper hose temp vs lower hose temp vs heater valve hose before and after then
radiator temp upper to lower. Thermostat housing vs water pump temp etc.


https://www.amazon.com/Etekcity-Lasergr ... 186&sr=8-3
thanks! another tool to add to the arsenal. I've wanted one for awhile, now it seems I have a reason to have one.


Thanks everyone for all the replies. As soon as I hear a good way to test radiator flow, that will be done and the electric fan issue is a priority. I'll see if I cant find a source or upgrade.

Jay
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85 M635
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Brucey
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Re: Help with hot running m88

Post by Brucey »

the best way to check the radiator for flow is to compare it with a new one of the same type on a test stand, i.e. to measure the pressure drop at fixed flow. Some radiator repair shops have such a thing but not all.

You can approximate to this at home by simply running a hose into one end of the radiator and allowing the water to exit the bottom. If (at a sensible flowrate) the radiator doesn't drain well enough to 'keep up' then it is almost certainly badly blocked. However this test is by its very nature approximate.

Another test you can do easily is to remove the viscous fan and cowl, get the car warm but not super hot, and then (with the engine running) spray the outside of the radiator with water. If there are any cold spots (with bad flow) these will show up by taking longer to dry off. If they are really bad they will (with the engine turned off so you don't get snarled up in the belts) feel cooler than normal to touch too. I say 'cold spots' but in reality they will be cold lines; if a tube is badly blocked there won't be enough flow down the length of that tube and the result is a cold line down the length of the radiator. There will of course be a temperature gradient down the length of these tubes anyway, (if the radiator is doing any useful cooling that is...) but this test normally shows blocked or badly flowing tubes quite well. What it doesn't do is show very clearly if the whole rad is only flowing half as well as normal, i.e. if all the tubes are half-blocked.

If the rad is only flowing half as well as normal, one symptom is that the pressure in the bleed hose will be abnormally high when the engine is running; asssuming it is flowing normally (i.e. it is not also partially blocked) then you can gauge the flow by looking in the header tank (with the cap off -careful now- and the engine warm but not hot). A vigorous flow indicates higher than normal pressure in that end of the radiator. Compare with another car of the same type.

Possibly there is a nominal (measurable) pressure which is unacceptably high, but this would also depend on the water pump. Most such systems have a fair amount of leeway built in; you can lose a good fraction of the tubes in a normal radiator and the system will still work OK under most conditions. In a way this is good, because if you have a cooling issue in normal running, the radiator has to be obviously faulty before it is likely to be the main cause.

cheers
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85MSteinway
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Re: Help with hot running m88

Post by 85MSteinway »

Brucey,
thorough. thanks!

Jay
L6
85 M635
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