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Post by wannabe on Jun 21, 2017 10:34:16 GMT
Ok, I am confused.com. (Not hard to achieve, admittedly...)
When I check the oil, one side of the dipstick can have oil up an over above the full mark, but the other side can have the oil level below the halfway line.
Or, like last night, below the minimum level on one side but seemingly over the full mark on the other.
WTF?
Which am I supposed to believe??
If I believe one side then my engine is about to lunch itself through lack of oil, but if I believe the other side, there's more than enough in there and all should be fine.
If I believe the former and add a litre of oil, then I could effectively be drowning it in oil by completely overfilling it when the latter side is correct! 
Is it just the case that the dipstick tube is curved at the bottom as it meets the sump and one side of the stick is therefore dragging oil up/from it because it's touching the side? In which case I should believe the side that is lower??
I thought I always had plenty of oil in it but skuzzle remarked it looked to be low when they checked it, even though I (thought I) had topped it up before setting off...
If it has always been low, perhaps because I'm looking at the wrong side or taking an average of the two), then that might explain why my oil pressure is often terrible at idle (but fine when moving)?
Why are things never simple!! |
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Post by atlex on Jun 21, 2017 11:02:23 GMT
don't take the first reading so seriously, IMO. My dipsticks always comes out too messy to read perfectly. usual job.. leave the engine off for 20 minutes or so. clean the whole dip stick off with a paper towel, put it back in, take it out, read it, take the reading averaged the two sides of the stick (they should be within 2mm of each other). if it is below the full mark, refill a little at a time (50ml?) and measure again after a few minutes. repeat. don't overfill it. don't stress unless your oil level is well below halfway between 'low and high' on the stick. do check for oil stains under your car's parking area  FWIW I check my oil once a week when I'm using mine. You'd be an idiot not to :-) oil pressure is normally low at idle (when warm) because the engine isn't turning that fast - this isn't a problem... it's the flow that matters, and the pressure should increase with revs as long as everything is fine. the oil pressure is a factor of revs and oil temp. the revs are what cause the oil pump to operate - it pumps faster the more revs you give it, which increases the flow (and by virtue of the oil galleries being a tight system, the pressure). when the oil is cold the pressure should be high even at low revs because it is thicker and as we all know. When the oil is hot the pressure should be low (but not nothing, mind you) at low revs, because it flows more efficiently (i.e. faster) through the oil system. I actually use the oil pressure gauge to measure oil temperature - you can work out when the oil is up to temp by when the pressure is low when it is idling, say at a stop light, at which point you know you can cane it. |
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Post by minty on Jun 21, 2017 13:24:16 GMT
^^this^^
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Post by joeytalent on Jun 22, 2017 16:22:37 GMT
Someone once told me to twist the dipstick round when it's when it's in place after cleaning it to get a better reading. No idea if that's good advice or not, but I always did it.
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Post by atlex on Jun 22, 2017 16:46:08 GMT
twisting the stick will just give you a more 'average' reading so not a bad idea. |
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Post by Rickster on Jun 22, 2017 17:48:43 GMT
leave the dipstick out for 5 mins - it allows all the oil on the side of the tube to run back down, then dip it in.
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Post by wannabe on Jun 22, 2017 17:54:28 GMT
Awesome  I'm guessing leaving it halfway in the tube is a good way to let the oil in the tube drain while not losing the dipstick by putting it down somewhere and forgetting lol |
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Post by Rickster on Jun 22, 2017 17:55:40 GMT
Awesome I'm guessing leaving it halfway in the tube is a good way to let the oil in the tube drain while not losing the dipstick by putting it down somewhere and forgetting lol You read my mind |
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Post by minty on Jun 22, 2017 19:58:29 GMT
So basically the advice is to 'double dip'  |
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Post by wannabe on Nov 8, 2017 13:57:19 GMT
don't take the first reading so seriously, IMO. My dipsticks always comes out too messy to read perfectly. usual job.. leave the engine off for 20 minutes or so. clean the whole dip stick off with a paper towel, put it back in, take it out, read it, take the reading averaged the two sides of the stick (they should be within 2mm of each other). if it is below the full mark, refill a little at a time (50ml?) and measure again after a few minutes. repeat. don't overfill it. don't stress unless your oil level is well below halfway between 'low and high' on the stick. do check for oil stains under your car's parking area FWIW I check my oil once a week when I'm using mine. You'd be an idiot not to :-) oil pressure is normally low at idle (when warm) because the engine isn't turning that fast - this isn't a problem... it's the flow that matters, and the pressure should increase with revs as long as everything is fine. the oil pressure is a factor of revs and oil temp. the revs are what cause the oil pump to operate - it pumps faster the more revs you give it, which increases the flow (and by virtue of the oil galleries being a tight system, the pressure). when the oil is cold the pressure should be high even at low revs because it is thicker and as we all know. When the oil is hot the pressure should be low (but not nothing, mind you) at low revs, because it flows more efficiently (i.e. faster) through the oil system. I actually use the oil pressure gauge to measure oil temperature - you can work out when the oil is up to temp by when the pressure is low when it is idling, say at a stop light, at which point you know you can cane it.
Ok... so.... to come back to this... (and with apologies for seemingly asking a neverending stream of annoying questions )
The bit in bold - how low is too low?
Ignoring the disappearing water issue in my other thread  I have concerns that my engine is on the way out, as once up to temperature, the oil pressure is sitting barely above the needle it rests on - perhaps 0.4 or 0.5 Bar  Sometimes it will sit at 1Bar, but it seems to have a mind of its own!!
If I left the revs from idle to about 1250rpm, the pressure will rise to about 1Bar, but that's not exactly a solution lol
It will go up to about 2.5 Bar when under load and going uphill, for example, but only ever reaches almost 4 Bar when stone cold and under load. (I'm using Asda 5w40 Fully Synthetic oil  that does need a change TBH).
It still pulls strongly enough (ignoring the blatant timing issue that is causing 'crackling' under load and a drop off of power at 6k rpm) and feels alright to drive, but am I looking at the dying days of an early 1.6?? Or is it just in desperate need of a service due to old(ish) oil taking in ambient moisture over time and getting thinner?
I hope it's not dying, I can't afford a new one and we can't fix the oil pump on the SNC engine
I had thought about swapping to 10w50, for example, but then surely thicker oil would put more stress on the ageing oil pump and kill it quicker, not to mention create drag in the engine and take longer to circulate when icy cold (speeding up wear)?
There's also the school of thought that says you either have oil pressure (and a working engine) or you have no oil pressure (and a dead engine), so if it's running, don't stress about it?
Any advice gratefully received!!
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Post by atlex on Nov 8, 2017 17:24:34 GMT
Cold start at 2-3K your oil pressure should be touch 4 kg/cm2 or over...
5w40 is perfect for UK temps, even winter ones.
2 choices : your sender or display unit are fooked or your oil pressure is really that low, in which case, ouch.
suggest you replace the sender and instrument bit, or at least look at the voltage you're seeing.. before driving it much more.
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Post by wannabe on Nov 8, 2017 18:09:04 GMT
Cold start at 2-3K your oil pressure should be touch 4 kg/cm2 or over... 5w40 is perfect for UK temps, even winter ones. 2 choices : your sender or display unit are fooked or your oil pressure is really that low, in which case, ouch. suggest you replace the sender and instrument bit, or at least look at the voltage you're seeing.. before driving it much more.
I guess the sender is probably as old as the car so that would be the easiest/quickest thing to replace, with a pattern part:
www.mx5parts.co.uk/pressure-switch-aftermarket-mk1-1994-1998-p-550.html £5.35 inc VAT
or, er, OEM...
www.mx5parts.co.uk/pressure-switch-genuine-mazda-mk1-1989-1994-p-853.html £114.28 inc vat !! 
The display does flick up and down slightly sometimes, but I'm not sure what that might be indicative of?!
I'm guessing I'll need a digital multimeter for looking at the dash - I have one somewhere, but it's not like I have a clue what to do with it lol
Thanks for the reply
I'll have to order the first one above and then add it to the list of things for the garage to do... lol
Everyone cross their fingers!!
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Post by martiny on Nov 8, 2017 18:25:56 GMT
There is a proper Mazda spec for how low is too low on idling oil pressure but sadly I can't remember where I read it. I recall it was either 2kg/cm² or 1cm/kg² (30psi or 15psi) and I guess it was the lower number but honestly I can't say for sure. Anyway if mine was reading sub-1kg/cm² I would first check the electrical connection on the pressure sensor and then maybe do an oil flush in case the pressure relief valve just after the oil pump is stuck open. PS wannabe - that first oil pressure switch you linked to is the simple on/off type for 1995+ dummy gauges, not the proper pressure sensor for earlier cars. PPS I should have a used sender in the garage. Somewhere. And a gauge. |
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Post by atlex on Nov 8, 2017 18:28:13 GMT
vindi and others may have spare senders. I've got a spare mk1 instrument bit somewhere. whisper (skidnation) over on mutts is making a new receiver/instrument bitthat is digital, too but only for NB, for now.
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Post by wannabe on Nov 8, 2017 22:07:28 GMT
Awesome replies, thanks chaps The difference in price on the two switches makes sense now lol I'll get searching on the recommended pressures. I didn't know there was a pressure relief valve?! An oil flush could be beneficial, might help clear my sticky HLAs as well... |
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I have concerns that my engine is on the way out, as once up to temperature, the oil pressure is sitting barely above the needle it rests on - perhaps 0.4 or 0.5 Bar 
Sometimes it will sit at 1Bar, but it seems to have a mind of its own!!
that does need a change TBH).
