Schitzo, Pshovest, Spirti Force, etc Temp vs Pressure update

[JimLev]

I posted some of this last week, it got buried pretty quickly. You were the main guys interested in this iinfo. Looks like the 1.2 Bar cap could present a problem with the tu motors running at 108°C on very hot days. See 1st post, I updated the info and also the attached pdf. http://forums.bimmerforums.com/forum...3#post25452593

[edjack]

Looks like some guys (not you, of course) are confused: The higher-pressure cap is used to prevent boiling, not to regulate temperature. The first place boiling occurs is in the head area surrounding the exhaust valves.

[motorade1]

Im confused, why would the 1.2 bar cap present a problem?

[JimLev]

Im confused, why would the 1.2 bar cap present a problem?

1.2 bar = 18 PSI
A 1.2 bar cap would vent and puke coolant. Maybe not in Canada or Alaska but in the south it could be a problem on the tu engine cars.

[pshovest]

More good info Jim. I saw your updated post in the other thread. We're in the very small minority of people who understand that the cap doesn't determine the operating pressure of the cooling system. Welcome to the internet.....where trying to raise the awareness level is a never ending, nearly imposssible task. I can't help but wonder how many of these radiator hose neck failures are due to damage caused by stresses that result from twisting and excessive forces used during removal of the hoses. Particularly with the o-ring style hoses. I finally replaced the original radiator and exp tank in the '00 wagon last summer after 148K miles. Only replaced because I was taking a 2000 mile trip. Temp was never over 97C the few times I checked. Of course the V8's run a lot hotter.

[JimLev]

When I removed my OEM radiator I also did find that the O-ring had pretty much stuck itself to the neck. After gently rocking it in all directions for a few minutes and then pulling it straight back it did come off. I should mention that I still have the original motor mounts which sometimes are blamed for snapping the necks. On the V8's BMW did redesign the top hose making it a bit longer to lessen the pull on the necks if the motor mounts are bad.

[rdl]

More good info Jim. I saw your updated post in the other thread. We're in the very small minority of people who understand that the cap doesn't determine the operating pressure of the cooling system. Welcome to the internet.....where trying to raise the awareness level is a never ending, nearly imposssible task.
...
Temp was never over 97C the few times I checked. Of course the V8's run a lot hotter.

This is an interesting thread, isn't it? Jim's measured data is especially illuminating - theory is good, data is better.
And I couldn't agree more about the rad cap vs pressure misconception that refuses to die. It brings to mind a game of whack-a-mole!

BTW, I'm pretty sure that V8s and I6s actually run at similar temperatures. I think the difference in observed KTMP is a result of the sensor in the I6 engines being located where it doesn't see the highest temperature in the engine, i.e. at the thermostat, while the V8 sensor is at the thermostat. See this link for an explanation with a little data that supports the hypothesis.
http://www.bimmerfest.com/forums/sho...9&postcount=10

Regards
RDL

[540ipaul]

Pv=nRT

[rf900rkw]

BTW, I'm pretty sure that V8s and I6s actually run at similar temperatures. I think the difference in observed KTMP is a result of the sensor in the I6 engines being located where it doesn't see the highest temperature in the engine, i.e. at the thermostat, while the V8 sensor is at the thermostat

I noticed this exact thing a few months back, a seriously forehead smacking moment. I was just in the process of digging up a picture showing the flow difference, and you beat me to the topic. See how the sensor is in the inlet (cold side) feed just before it's dumped into the back of the head.

m54-coolant-flow.jpg

[rdl]

I noticed this exact thing a few months back, a seriously forehead smacking moment. I was just in the process of digging up a picture showing the flow difference, and you beat me to the topic. See how the sensor is in the inlet (cold side) feed just before it's dumped into the back of the head.

m54-coolant-flow.jpg

That picture is exactly what triggered the same FSM for me too. I'd forgotten where I found it. It's a good addition to the thread.

Regards
RDL

- - - Updated - - -

Pv=nRT

I don't understand the point you're making. It seems to me that the physics involved in determining cooling system pressure is of partial pressures of vapours over a liquid at various temperatures. Different from the pressure - volume - temperature relationship for a gas/vapour with no liquid phase present, which is what the ideal gas law describes. What am I missing?

BTW, a point of clarification. I think you mean PV=nRT for the ideal gas law.
The convention is upper case V => volume in litres, m3, ft3, etc., while lower case v => specific volume in m3/kg, ft3/lbm, etc. (an alternative statement is Pv=RT, n being the # moles, mass etc., n being divided into V to yield v)

Regards
RDL

[rf900rkw]

It's from the E46 introduction training manual, chapter 9. Here's one other diagram from that which applies here, but I'm going to use it to go off topic a bit.

m52tucoolant-flow.jpg


As oft repeated, TIS says to pour some coolant in then start the motor and rev the piss out of it. In the "good" old days when the lower hose fed directly into the waterpump, this worked great. But with the advent of the blending thermostat designs, the waterpump feed now comes from the top... where the air is. And with the M52tu onward, the effluent also goes straight to the top. Revving the crap out of a waterpump with both it's inlet and outlet airlocked isn't going to accomplish much, I dare say.

[motorade1]

So I put in a question to German Auto Solutions and this was their response:

In a properly filled cooling system the pressure never exceeds 1.0 bar under
any normal operating conditions. The vehicle has to overheat to the point
that the temp gage is pegged, to exceed 1.2 bar. The cap prevents excessive
pressure from exploding your radiator, hoses, expansion tank or thermostat
housing if your cooling system fails in some way and engine overheats. It
also vents excess pressure, preventing damage to your cooling system
components, if you accidentally over fill the expansion tank.

Gary Geukes

German Auto Solutions

Thoughts?

[JimLev]

. Revving the crap out of a waterpump with both it's inlet and outlet airlocked isn't going to accomplish much, I dare say.

This is why I'm always telling people to remove the bleed screws and fill those sections with coolant. It's a frigging water pump not an air pump!

- - - Updated - - -

So I put in a question to German Auto Solutions and this was their response:

In a properly filled cooling system the pressure never exceeds 1.0 bar under
any normal operating conditions. The vehicle has to overheat to the point
that the temp gage is pegged, to exceed 1.2 bar. The cap prevents excessive
pressure from exploding your radiator, hoses, expansion tank or thermostat
housing if your cooling system fails in some way and engine overheats. It
also vents excess pressure, preventing damage to your cooling system
components, if you accidentally over fill the expansion tank.

Gary Geukes

German Auto Solutions

Thoughts?

Gary is a pretty sharp guy, however how can you say that on a 99-100F day driving on the highway, not stop and go city traffic, that this isn't a normal driving condition with the KTMP reading 106C. The 18PSI gauge reading is 1.2 bar. This isn't a cheapo gauge either so I believe the readings.
I've seen the coolant temp as high as 110C before stuck in city traffic, didn't have a pressure gauge installed then but I'd venture to say that it was above 1.2 bar. Your located in SC where it is generally hotter than up here.
Its your car and I wish you well with a 1.2 bar cap. I think the 1.4 bar cap will give you a little more of a safety margin.

RLD, good info in the link you provided.

[rf900rkw]

Jim -- I have found that the bleed screw borders on being virtually useless. Apparently Zionsville agrees, as they don't bother with one on their replacement systems. The cooling system is/was constantly evolving and there are many different layouts in the E36/39/46/53 series. But from what I've seen all the bleed screws share a common trait. There is an air purge hose from the top of the hot side radiator tank to the neck of the filler. This passage Y's at the expansion tank. One side enters the neck between the two o-rings on the filler cap and the other goes to the bleeder. The cap blocks the passage at the neck. With the cap on, the bleeder can be used to vent any air trapped at the top of the radiator, but mostly hot coolant all over the engine bay. But when the cap is removed during filling, the bleeder port is redundant; the passage is already open.

A thought that just occurred to me. The lower o-ring on the cap is important. It keeps the passage sealed and prevents a back-syphon of the air in the expansion tank back into the radiator while the system is off.

On the 1.2 cap. If you have ever witnessed a true boil over, you'll understand why this is a bad thing. When the radiator cap releases due to boiling, The pressure drop causes even more boiling which continues the release... until a large percentage of the coolant is on the ground. I suspect many envision a cap release on their baby as a little bit of drooling on the chin. Not so. It's more of a bazooka-barf, spewing puree of spinach everywhere. Dropping the cap pressure on a working system will do nothing. Dropping the cap pressure on a failed system *may* protect some components at the expense of putting you on the side of the road. Dropping the cap pressure to the verge ofcausing system failure is just plain dumb.

[JimLev]

All good info. The 1.2 cap is a crap shoot. I do have a 1.4 cap but think I'll stick with my 2.0 cap. On the bleeder screws I was referring to the ones that are either on the t-stat housing or the one on the top radiator hose elbow. Most of the time after refilling those I6 systems this section doesn't have much, if any, coolant in it. On the V8's after filling the system thru the expansion tank I disconnect the top radiator hose and pour in another quart of coolant. After doing so I don't need to bleed my system.

[pshovest]

Interesting indeed. Finally an explanation for the apparent difference in KTMP's. I'll have to drag out the TC adapter for the Fluke. I think I can squeeze the TC junction under the hose clamp. I don't trust those laser pointer IR Temp readers.

This is an interesting thread, isn't it? Jim's measured data is especially illuminating - theory is good, data is better.
And I couldn't agree more about the rad cap vs pressure misconception that refuses to die. It brings to mind a game of whack-a-mole!

BTW, I'm pretty sure that V8s and I6s actually run at similar temperatures. I think the difference in observed KTMP is a result of the sensor in the I6 engines being located where it doesn't see the highest temperature in the engine, i.e. at the thermostat, while the V8 sensor is at the thermostat. See this link for an explanation with a little data that supports the hypothesis.
http://www.bimmerfest.com/forums/sho...9&postcount=10

Regards
RDL

[rf900rkw]

Out of the five BMWs in my driveway, plus the E53 I put a radiator in yesterday, none of them have a bleeder anywhere except on the expansion tank. I agree a select few have a bleeder in a place that makes sense from an initial fill standpoint, but it isn't the norm.

[philly98540]

In regard to the pressure build up, besides the vapor pressure, you also have the expansion of the coolant in a sealed system. Glycol expands a lot. The air that is trapped in the closed system absorbs this expansion like a spring. If you have a really full expansion tank and a well bled system with minimal trapped air pockets, then the system pressure will build higher than an identical car that had more air originally in the system.

If the pressure, due to this expansion, exceeds the cap rated pressure, then some air can be expelled without a boilover happening if the coolant is still below the boiling point at this release pressure.

So, I think a 1.0 (or 1.2, 1.4) bar cap may just burp out a little air when the pressure builds as long as the hottest point in the engine coolant passages is still below the coolant boiling point at the cap release pressure. When the car cools back off, the cap allows the air to come back in. If the hottest part of the motor exceeds the boiling point during this release, then you get the huge boilover situation. Not good.

I think BMW used small(ish) expansion tanks on the E39 and may have put higher pressure caps to keep the system sealed at all times. It they had a larger air pocket in the expansion tank, the pressure would not build so high due to the expansion. They also run these engines hotter than some other manufacturers. I believe the expansion tank size combined with the higher running temps forced BMW to run the high pressure caps to be sure the system remained sealed at all times.

The vapor pressure (due to the coolant being heated) adds to the compressed air pressure (due to the expansion) to give the total system pressure. I believe this is the rule of partial pressures if I remember correctly.

[Schitzo]

1.2 bar = 18 PSI
A 1.2 bar cap would vent and puke coolant. Maybe not in Canada or Alaska but in the south it could be a problem on the tu engine cars.

Hi Jim thanks for the updated numbers. While the 1.2 bar seems low, it is the norm for many auto manufacturers. In fact BMW has now gone back to using 1.2 bar and 1.4 bar caps in the newer models including V8s.