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dtharp113

Cooling system conundrum

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Am vexed by my cooling system: I replaced the t-stat in my '74 (the new stat is a 75). Since replacing, my temp gauge has been showing low (150's) temp, my oil pressure has been on the high (approx 30 while idling/ 50+ while driving in 5th gear). This is a change from my original numbers of 180°/ 30lbs.

Some additional data (because I know someone will ask…):

3min after start: top hose=70°; tstat housing = 79°; lower rad hose=68°; oil press = 70

15 min idle: top hose 148°; tstat housing 122°; lower hose 109°; oil press 30 (at idle)

after 20 min drive: top hose 151°; tstat housing 132°; lower hose 128°; oil press during drive approx 50lb. Engine block temp was measured at 185°

I'm confident that the system has been burped, and I have good heat from the heater core. I'm feeling that these numbers are too low/high and a search of the FAQ confirmed this.

My question is: should i swap out the current thermostat for a different temp (and if so, do I go higher (to 85) or lower (71°)? I've not found a good explanation of what temp thermostat one should run with in the FAQs. I'm not sure if another possibility would be a bad temp sensor/sender. If so, how would one test for that?

Thanks,

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(edited)

I've been using an 80 thermostat for 3-1/2 years and all temps are "normal" ..... which means the temp needle never goes above 3 o'clock.

      Funny also:  on cold mornings the temp needle is at 3 o'clock.  Later in the day when the air temp is in the '80's, the temp needle is at 4 o'clock (engine running "cooler").   I can't figure it out, but don't need to:  engine temps are where I like 'em to be.

 

For years I used a 75 thermostat and the engine ran a bit hotter.  I decided to try the 80 and prefer it.

 

Cheers,

 

Carl

Edited by OriginalOwner

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I believe 185 is 85 Celsius

As long as your temp goes back down after therm opens, all is ok

I know it can be difficult to find a Celsius gauge, but it would be so much

easier to follow what your thermostat/coolant temps are

With a good radiator, you can use 71, 75 or 80 deg thermostats,

depending on your weather. Obviously 80 deg keeps you warmer in winter.

I almost always use a 75 but have had 71 and 80 as well.

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I was using an IR thermometer to check the hose/thermostat housing temps, and the stock temp gauge hasn't worked in a quite a while (that's why I have a VDO gauge installed).

So, from what i can gather from the replies, it sounds like I have the wrong temp thermostat installed.

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75c =170f   Pretty chilly.  And sometimes they are a bit off, as in, a little low or a little high.  Yours sounds a bit low...

 

t

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Engine block temp 185 deg F, what's wrong with that? The block and head temp are what matters.  

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(edited)

I'll submit my own Quite Philosophical Hypothesis that "wrong" is the wrong word.  It's a matter of making things work for your own comfort zone.  

     These engines, as are all engines (and mechanical systems in general) a confluence of many mechanical parts, and I'm fully convinced that when all assembled into the greater whole, they are imbued with a bloody mind of their own as to what they want to do and how they are going to do it.

     I've seen Fords and Chevy's and Triumphs and Datsuns and whatevers, and they are all over the map for specs and actual temps and thermostat ratings and whatever.  They all run, but sometimes they just don't make sense that they should be running as they are.

     So I've simplified my life and discovered a personal comfort zone that makes me happy because my '74tii has not (yet) exploded or melted in that existential process.  And these days, my thermostat has communicated to me that it likes being an 80 .... and I'm not necessarily being asked to like it, I'm simply required to accept that at this finite point in time the confluence of parts under the hood desires it.

 

Such can be the ways of the Zen mechanic .....

 

Cheers,

 

Carl

Edited by OriginalOwner

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Clyde Bobard uses an 80

 

because that's what works for him in nebraska

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I've been running an 80 degree (Celsius) 'stat since 1987, when I installed a three row core radiator.  Car has A/C, and has been all over the country including triple digit air temps--about the highest temp gauge reading I've seen is about 2 o'clock and that only on a very hot day, on the highway with the A/C running full blast.  When I rebuilt the engine (tighter clearances thus more friction) the engine didn't run any hotter.  And yes, I've checked my gauge reading against a mechanical gauge and it's accurate.  

 

But as has been pointed out, it seems each M10 has a mind of its own as to what 'stat it's happy with.  My '69 also runs an 80 degree  'stat and runs consistently cool (needle is about 3:30).  Rarely gets above 3 o'clock.  Go figure.

 

mike

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Right, so let me see if I'm understanding this (there's a reason why I was a liberal arts major and not an engineer…) the higher the Celsius rating on the thermostat, the higher the water temp needs to be open said t-stat, which means the engine runs warmer (than if one used a lower C rated t-stat), which means in hotter areas one would use a 71 and in colder areas of the country an 80. Correct?

Part 2 is my puzzlement over the 30° delta between the radiator hoses and the engine block and why my water temp is not getting over 150°. Could the lower water temp be a result of the thermostat

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(edited)

 ummm, yes and no, but essentially not really ........ the thermostat is merely a mechanical temperature sensing device.  When the coolant surrounding it reaches the "set temperature" of the thermostat heat thingie, the heat thingie opens, letting more cool-temp coolant from the radiator pass through and into the head/block.  

    Ideally, you want the incoming coolant temp to be "well below" the set temp of the heat thingie ..... which means you want/need a radiator that does a great job of removing heat from coolant.

    OK, with all that, the theory goes that the incoming cool coolant will cool down the now-heating-up coolant in head & block.  That now-heating-up coolant goes eventually to the radiator, cools way down, then gets flowed back as necessary into the head/block to cool down the hot stuff.  Capische ??

    Ideally and in theory and in practice and in operation, the entire cooling system will find it's own thermodynamic equilibrium, and said equilibrium is maintained by the overall thermostat operation & function. 

    Thus, if you install a 71-deg thermostat, theory says the system will run at 71-deg ..... sorta/kinda/somewhere.  Yeh, right, because the math tells a very different story.  And whether it runs at 71-deg at your temperature sensing device, who knows.  71-deg just means the thermostat is gonna theoretically open itself up a bit and let some cool coolant pass on through and go somewhere.  Same theoreticals of course apply for an 80-deg thermostat.

     As for "when" to use a different temperature level of thermostat, that is personal preference for whatever you want your 2002 to do, wherever/whenever/whatever.

 

as for your Part 2 ..... that would be all part of whatever your overall coolant system wants to do as it finds it's own state of thermodynamic equilibrium during operation.  Does it make sense ??  If not, please refer to what I wrote way above .....  OHMMMMMMMMM .......

 

Cheers,

 

Carl

Edited by OriginalOwner

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(edited)

The only thing that matters is the block/head temp.  The cooling system on a BMW 2002 and most, if not all other BMW's, is what I would call a bypass type of cooling system.  This means that if the engine is not warm enough, the thermostat bypasses the radiator and allows varying amounts the coolant to be re-circulated from the cylinder head back to the pump, and then through the block and head without going through the radiator.  The reasoning behind this is to keep the coolant velocity through the engine as high as possible, to prevent hot spots in the block or head.  All your measurements are just the result of this process.  You don't need a lower temp thermostat  because you live in a higher temp area.  The thermostat you’re using will take care of that as much as possible, unless you have a plugged radiator or water pump with halve the vanes corroded away.  

Edited by allbim

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