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Author Topic: A question on ail pressure and thermostat?  (Read 2767 times)
davidewanprice
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« on: May 30, 2008, 06:08:39 pm »

Two questions for you all, as you all know by now im not that well up on engines but obviously want to make sure i can read how my car is in turms of watching the guages.

Oil pressure? what figures do you guys get. I'm get a higher reading (if i remember 3) when the engine starts and when fully warmed up it falls, sitting just above zero only rising when you hit the loud pedal hard.. To me this seems norm, in that the oil thins as it warms causing less pressure.

Secondly, whats the best way of testing your thermostat is working in your car. I ask because i cant remember the last time i heard my fan kick in (I do however have a manual override). Obviously i am i safety boy and when im in traffic i just automatically turn it on if it gets near 90 degrees. I was under the impression at this temp it should kick in... Thanks guys...

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macaroni
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« Reply #1 on: May 30, 2008, 08:08:16 pm »

I get a higher figure than that. When cold, and revved hard it goes up to 8.

My temp fan kicks in just above 90, so in heavy traffic, the gauge hovers around the 90 mark.
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Anders Dinsen
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« Reply #2 on: May 30, 2008, 08:41:50 pm »

Fan kicking in can take a while in my experience. I'm paranoid and flips the override as soon as I'm not moving or going slowly and the temperature crosses the 90 degrees mark. With the engine rev'ing, my thermostat usually keeps the engine below 90.

About the oil pressure, I think your sender could be working badly as it drops to only just above 0 when fully warmed up. Mine is seldomly under 1. But mine starts at 3 when cold too. This is the pressure at idle and with 5W/50 synthetic oil. That's a guite "thick" oil when hot.

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roy4matra
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« Reply #3 on: May 30, 2008, 08:57:23 pm »

Oil pressure? what figures do you guys get.

A new (or good) Murena 2.2 should give at least 3 bar hot idling, and would go up to maximum (7 bar?) once revs were up above say 2500 - 3000 rpm.  Obviously this will also depend to some extent on the particular oil being used.

I used Mobil SHC from the start in '83, until it changed name to Mobil 1 later.  At first I think SHC was rated as a 10w-50, then it changed over a period especially after it became Mobil 1 and now the one you should use is the 15w-40 not the 0w-30 or whatever is the standard version.

As I didn't like the way it dropped in rating to match the latest engines, I switched to Castrol RS which is a 10w-60 rating and still got good pressure.  However, I have found that after a crank regrind many 2.2 engines suffer lower oil pressure compared to the original.  I assume this is due to larger tolerances.

I have recently had an engine machined for overhaul and asked them to make sure the tolerances were small, as I was prepared to run it in carefully.  It will be interested to see the oil pressure on this engine when it is finally run.

Quote
I'm get a higher reading (if i remember 3) when the engine starts and when fully warmed up it falls, sitting just above zero only rising when you hit the loud pedal hard.. To me this seems norm, in that the oil thins as it warms causing less pressure.

That is only really true of a non-synthetic David.  It is the waxy element that makes it thick when cold and less thick when hot.  A full synthetic does not have this waxy element (which you don't want) so the pressure stays more consistent from cold to hot.  Mine never varied noticeably at all, but my engine had never been stripped, reground or rebuilt.

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Secondly, whats the best way of testing your thermostat is working in your car...

If you mean without taking it out, then just watch the gauge.  If a thermostat and cooling system is working properly, then when cold and the thermostat closed, the engine should warm up quickly as it is only circulating in the block, and the radiator circuit blocked off.  Once it reaches opening temperature, and the cold coolant from the radiator is introduced the temperature actually drops back slightly before rising again to stabilize at the thermostat setting.  I have seen this even on Murena gauges (both mine, and Brians which I looked after for some time) so I know it can be detected.  The temperature it will open or stabilize at, will depend on the thermostat rating.

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I ask because i cant remember the last time i heard my fan kick in (I do however have a manual override). Obviously i am i safety boy and when im in traffic i just automatically turn it on if it gets near 90 degrees. I was under the impression at this temp it should kick in...

The standard Murena cooling fan switch is a 95/85 setting, meaning it will cut in at 95 degrees and cut out again once it is down to 85 degrees, so provided your switch is standard these are the temperatures.  However, you can get different switches, such as 92/82 or 96/86 etc.

If you switch your over-ride in all the time at say 90, which is lower than the switch, then not only will the switch never get chance to work, but the chances are that it may not work when it does reach the required temp. as it will have become 'stuck' from lack of use.  You should ideally let the switch do it's job normally, for minor hold ups like say in stop, start traffic where you can see you will not be held up for long.  I would suggest only using the over-ride if you can see the traffic jam is something major, and you are likely to be stuck for some considerable time - then you can hit the switch and stop the heat build up in the first place.  Obviously any time the temperature goes above your switch setting without the fan cutting in, you need to hit your over-ride, and remember to find out later why it didn't work.

You should always test the switch at any major service, by letting the heat build until it cuts in, but if it reaches say 98-100 degrees (which is still safe) and it hasn't cut in then either switch off, or if you have an over-ride then use this to drop the temp. back down.  Then once it has cooled you need to find why it did not work. (remove and test)

Roy
« Last Edit: May 30, 2008, 08:59:37 pm by roy4matra » Logged

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