Can over cooling be caused by air?

[doogie]

I know most mentions of lack of correct bleeding revolve around over-heating.... I have over cooling - my temp gauge never reads 12, always the tick before that, so I read through the advice here and assumed a bad stat (I've already replaced it but with a cheap one) so I just bought a new stat from the dealer and installed it and still same problem. One thing though, my thermostat cover's bleed screw is jammed in tight and the nut is worn away.... I tried with WD40 and pliers and various things and I just could not get it loose, so I can't bleed from the stat housing - is an air bubble there likely to be causing my problem? I'm going to call the dealer today and see if they've got a new cover in stock (I ordered in and got a new bleed screw but I cannot get the old one out at all).... do you think that will solve it or am I barking up the wrong tree completely?

Thanks

Doogie

[philbyil]

Don't drive yourself nuts....a tick before 12 (11 oclock) is just fine!
Mine was always this way (for 7 years!) until I changed my water pump and thermo...it now shows 12.00. Didn't worry about that either :)

[Kalevera]

Yeah...that's completely normal...

[liquidtiger720]

mine is a whole needle width over 12. =)

[Hector]

to get the most from the engine. The engine control management system is designed to work with a thermostat set to a specific temperature whether it's 88 C or 82 C (or 81 C I think). A temperature that is constantly lower than this may not allow the computer to control the engine properly for operation at peak performance. Maybe others here on the board may have additional insight.

Here's an excerpt on a similar topic
http://www.northstarbmw.org/index.aspx?ns=TechArticles

"Thermostats maintain the correct temperature for both the passengers and the motor. If your thermostat is allowing your engine to run cooler than recommended the engine computer may never allow the fuel injection to work properly, causing poor fuel mileage, high emissions, poor performance and possibly fuel dilution in the motor oil. Typically, you would see this as a drop in engine temperature in cold weather, especially in highway driving. In the last few years BMW is using a computer controlled thermostat to allow for tighter control of engine temperature. This is done by building a "normal" thermostat that runs at a very high temperature. Incorporated in the design is a very small electric heating element that is controlled by the engine computer. By using the coolant temperature sensor as a feedback signal the engine computer can regulate the engine temperature by supplying current to this heating element as needed to cool the motor. Unfortunately BMW missed the mark in an early design of these thermostats on the six cylinder motors. An unacceptable level of failed thermostats has led to many cars being recalled to have the thermostat replaced with the newest design. Owners of affected vehicles will receive a notice in the mail from BMW."

[ryan roopnarine]

normal. in fact, if i were to go drop some watter wetter in my antifreeze right now, i could consistently get it to stay at 1 notch below for the next 5k miles. right now, it sits at 12, and may go down to 1 below if its colder than 40 degrees F outside, or if i've been letting it loaf on the highway for an hour or two.


I know most mentions of lack of correct bleeding revolve around over-heating.... I have over cooling - my temp gauge never reads 12, always the tick before that, so I read through the advice here and assumed a bad stat (I've already replaced it but with a cheap one) so I just bought a new stat from the dealer and installed it and still same problem. One thing though, my thermostat cover's bleed screw is jammed in tight and the nut is worn away.... I tried with WD40 and pliers and various things and I just could not get it loose, so I can't bleed from the stat housing - is an air bubble there likely to be causing my problem? I'm going to call the dealer today and see if they've got a new cover in stock (I ordered in and got a new bleed screw but I cannot get the old one out at all).... do you think that will solve it or am I barking up the wrong tree completely?

Thanks

Doogie

[doogie]

I've explained myself badly; by a tick I meant the next white line, 1/4 of the way up the scale. :(

Could that be caused by air in the system? I've ordered a new stat cover which will be in tomorrow so I will be able to bleed there tomorrow.

[Kalevera]

Oh...that happened to me a few weeks ago when I replaced my tstat...The problem turned out to be that I'd installed the new TSTAT rubber o ring incorrectly (wrong side). With the old tstat, it worked fine...the new one would creep to 3/4.

There's a huge thread on this I wrote a few weeks back..."cooling system problems :("

Here's what I did (in short):

- Drained the rad
- Pulled the tstat housing
- Reseated the tstat, put it all back together.

Since you have an M20, it may be different...I bet your exp tank is integral to the radiator. But you've got to be able to bleed the sucker. (also not sure if this applies to m20's): drill a 1/16" bleed hole due north on the tstat. Made my bleeding process effortless.

Best, whit

[Dash01]

Rather than replacing the cover, you could remove it use penetrating oil from the bottom side of the screw. If that does not work, consider re-tapping the hole for a slightly larger bleed screw.

Back to the over-cooling issues: Once you have the bleed screw made usable, do the bleeding thing and check temp. If still running cool, check the temp sender. Could be, the temp sender is sending erroneous input to the gauge, or the gauge is off a bit, rather than an overcooling situation, per se.

[doogie]

I've replaced the temp sender already, and when I short it the gauge goes to 100%.... I do think it is over cooling a bit because as far as I can tell it smells too rich... but I have thought the gauge could be a bit iffy. I'll have a look in Bentleys to check resistances of the sensors at various temps.

[632 Regal]

im confused.... are you at 1/4 or 3/4? From what I read it seems you are running cold, at 1/4. cold is better than hot but is also really bad for the engine cylinders in a wear standpoint. Air in the system wont cause this. Still sounds like a bad thermostat man, get a BMW stat with the little ball and tube deal spot welded to it and then the chance of getting a bad one is a LOT less likely. Since you changed the sending unit I'd bank on a bad stat...again.

[doogie]

I'm at 1/4, so showing as running cold. I had a french branded thermostat in there (think it was calorstat), replaced it with a £10 one from local Halfords which was the same brand, then replaced it with a £20 german branded one from the BMW dealer, which doesn't have a little ball and tube in it, but it was from the dealer...... :(

[doogie]

OK, been out and changed the cover over so I can now bleed at the stat housing :) (the stat from the dealer is branded Wahler)

Surprisingly enough, no change.... enging still running too cold according to the gauge (which I do need to check still).....

I've looked at the exploded diagrams and read through howstuffworks about car cooling and stats etc, and I'm still not sure how it all works :( the stat just stops the cooled water from the radiator return going into the flow, doesn't it? so the radiator top hose isn't blocked by the stat at all (is it pressure or water pump related that it doesn't flow through there or what? :confused:

Is there anything obvious I can check (apart from the gauge) before I think about going and buying *another* stat, my stat is in the right way according to the diagrams, although I've got it with the arrow facing up, so the pyramid bit is across the way and not up and down the way like shown on http://www.realoem.com/bmw/showparts.do?model=HB12&mospid=47369&prod=19890200&btnr=11_0788&hg=11&fg=35


Thanks

Doogie

[George Davis]

Near as I can tell, the cooling system in the '94 525i is set up with the thermostat blocking the return hose from the radiator, rather than (what I consider) more normal system where the t-stat blocks the delivery hose to the rad. While warming up, coolant circulates in the block and head, and some heat seeps up the hose to the rad even though there isn't any flow. Once the t-stat opens, coolant gets pushed through the rad in the usual manner. I'm also guessing the t-stat closes off the block/head recirc passage when the engine is warmed up.

Aside from that, I suggest you call around and try to find a repair shop or radiator shop that has an infrared thermometer and is willing to read your top hose temp for you. (You can buy one, of course, but unless you plan to use it a lot I'm not sure they're worth it). Get the car fully warmed up, 15 to 20 minute drive, and pop in there and have the temp read on the top hose, close to the block. This should tell you fairly accurately what your coolant temperature really is and help eliminate a lot of guess-work.

Good luck.

[liquidtiger720]

I should probly make my own thread, but is a needle width over 12 o'clock necessariy bad?]

~sorry for this OT/post jacking post.

[Mr. BILL]

I should probly make my own thread, but is a needle width over 12 o'clock necessariy bad?]

~sorry for this OT/post jacking post.


No. As long as it stays there you're fine.

[pong]

im also there... then one day... it suddenly jumped... had to change the cyl head gasket :z

[Kalevera]

Does it stay cold all the time or does it fluctuate depending on how you're driving (city stop and go vs. highway)?

If it's fluctuating, then something's up with the tstat (even though you've replaced it a billion times) or tstat housing. Mine did this when the tstat got stuck open (so it got really cool when moving at highway speeds, and got warm when sitting at a stop light.

There's really not much to the cooling system circuit here that could be attributed to your problem. If it's closed or your cylinder head has a problem, it overheats. If it's always open, it overcools.


best, whit

[doogie]

Does it stay cold all the time or does it fluctuate depending on how you're driving (city stop and go vs. highway)?

No, stays cold all the time.... if it was getting to 12 o'clock it would be perfect.... it's pretty much rock solid on the 1/4 way mark.

[doogie]

Near as I can tell, the cooling system in the '94 525i is set up with the thermostat blocking the return hose from the radiator, rather than (what I consider) more normal system where the t-stat blocks the delivery hose to the rad. While warming up, coolant circulates in the block and head, and some heat seeps up the hose to the rad even though there isn't any flow. Once the t-stat opens, coolant gets pushed through the rad in the usual manner. I'm also guessing the t-stat closes off the block/head recirc passage when the engine is warmed up.

Aside from that, I suggest you call around and try to find a repair shop or radiator shop that has an infrared thermometer and is willing to read your top hose temp for you. (You can buy one, of course, but unless you plan to use it a lot I'm not sure they're worth it). Get the car fully warmed up, 15 to 20 minute drive, and pop in there and have the temp read on the top hose, close to the block. This should tell you fairly accurately what your coolant temperature really is and help eliminate a lot of guess-work.

Good luck.

Thanks - that sounds like a very good idea.... I'll see who I can find locally that's friendly
:)

[Javier]

tstat is OK and tstat housing cover is OK, if cold, tstat would simply close rising temp.

It should be a metering error, I mean, sender unit (you change it already), wiring defects, or even gauge miss-adjustment.

There is an easy check, just unbolt sending unit (or get the old one that seems to be OK as problem continues), keep it plugged in the connector, look for a camping stove (or other means of getting boiling water), pan, water, a cooking thermometer 0-100 degrees C, turn key to energize gauges, and check your gauge readings at various temperatures from 0 to 100. (if no thermometer, at least you know boiling is at 100, and its pretty close to 1/2 (center gauge is about 84, 100 is about one needle past center).

This is what I would do myself, not having handy the sophistication of an infra red gun. Also this will confirm your metering system is/is not OK.

This link should help.

http://www.bmwe34.net/e34main/trouble/Data/gauge_overheat.jpg

Javier




No, stays cold all the time.... if it was getting to 12 o'clock it would be perfect.... it's pretty much rock solid on the 1/4 way mark.

[Dave M]

Well everyones hard at it, I may as well add my $0.02. Whether (pardon the pun) its +30 degrees celcius (90 F) or - 40 celcius (_40 F), the needle in my 91 525 sits at 12:00. If Javier's proposal doesn't provide the answer, its hard to ignore the thermostat. Is is possible to test these thermos in the classic " heat some water and drop the thermo in"? This may tell you if its a bum one and save time lookng elsewhere. Someone may know if this trick works.

Good luck,

Dave M

[632 Regal]

that trick works, the thermo should not open up at all untill the water gets damn hot, just before boiling since they are supposed to only begin to open at their specified temperature rating. You can get a candy thermometer at almost any hardware store for a few bucks and throw that in the water and really see whats going on, and then you can drill a hole in your smoker/bbq and use it there for perfectly smoked ribs! mmmmmmm.

[Javier]

weeks ago, this confirmed the tstat was OK (wrongly mounted, though).

Javier

[Kalevera]

True.

[doogie]

OK..... did some messing today.... put brown sensor in a cup of just boiled water, powered up car, barely moved needle. Tried shorting the connector and the needle also barely moves.... looks like a wiring fault somewhere..... d'oh!

The brown sensor has a brown earth and a brown/yellow wire coming from it. The connectors on the back of the instrument cluster don't have a brown/yellow wire on them... from what I can see I should be looking for a brown/violet at the instrument cluster end..... anyone tell me (or point me to the page in Bentley) that shows me where the brown/yellow goes before it ends up in the instrument cluster so I can find where the break/ problem is?

Thanks :D

[632 Regal]

might be a dash capacitor if you dont find a short.

[Javier]

I only have info for 525i and 535i that year. But the 1994 European wiring in this link:

http://www.carsoft.ru/avtorepair/bmw_e34/6200.3/index.html

reveals a brown/violet wire all the way to the instrument cluster (Pin X16-4).

In 1989 USA cars, the sensor is wired with Brown/Violet and Brown/Yellow wires all the way to the instrument cluster. Brown/Yellow gets ground from the cluster to the sensor, and Brown/Violet send back the variable resistor signal to the cluster, pins X16-24 and X16-26, but again, I understand that 520i instrument cluster is not the same that 525i/535i.

Did you check resistance to ground in both wires at the sensor? Are you sure Brown/Yellow is the signal wire? May be it is intended to be grounded and is opened! The said brown wire, wasn't Brown/Violet, and may be worn out the violet strip? Is it grounded? Have you checked continuity from Brown/Violet wire at cluster connector, and wires at the sensor?

Javier