fluctuation oil pressure

m ex 5 · Post by **m ex 5** » Wed Jul 19, 2006 10:10 pm

hi all, i was road testing an MX5 recently and while driving the oil pressure guage was wandering all over the place, is this normal/OK??? I have never had a car with one and not sure if I should be worried about buying the car, my first MX........ pretty tidy car so serioulsy interested about the only real worry apart from this is the cam belt has never been replaced (car has 130 Ks) and I have read it should be changed at 85! its one of the very first ones 89 so is there anything else I should look for??? thanks for taking the time to help.

Post by **jif** » Thu Jul 20, 2006 8:17 am

The 1600s have a proper oil pressure gauge so the fluctuation is normal - in fact people like me will spend good money to retrofit it into the later models!

Sounds like the cambelt will need attention, but if it breaks nothing serious happens.

So whatcha waiting for ?

[Posted via External Email]

Fletch · Post by **Fletch** » Thu Jul 20, 2006 10:05 am

The oil-pump is driven by the crank-shaft..... as rpm increases, the pump spins faster, and oil-pressure increases.

Also, oil's viscosity (thickness) reduces with temperature... when cold, idle RPM will give a higher pressure reading, than idling when warm....

Those two facts should account for all the pressure fluctuations you see.

ie. its totally normal.

Fletch.

Post by **simple** » Thu Jul 20, 2006 10:22 am

Assuming it's rpm-related, changing oil pressure is normal. Higher rpm
gives you higher pressure. Note that some later model mx5s don't have a
real gauge - it looks like a gauge, but really it is just saying that
there is *some* oil pressure, not how much.

When hot, the pressure should be somewhere around 2 at idle. This is
the easy way to know when your engine is truly up to temperature (the
water temperature gives you a clue, but water temperature is up to hot
before oil temperature, so water temperature alone is not reliable).

When cold, idle pressure will be somewhere higher (maybe 4? I haven't
paid much attention).

Non-rpm-related pressure wanderings could be a matter for concern. I
had weird pressure variations once when my oil level was very low.

I've started a new subject for discussing MX5 buying tips - find it here:
http://www.mx5forum.co.nz/viewtopic.php?p=12360#12360

Karl.

[Posted via External Email]

m ex 5 · Post by **m ex 5** » Thu Jul 20, 2006 12:00 pm

All great news, thanks to all for the input, i really wasnt sure so it's good to KNOW

thanks to all.......and what am I waiting for.... the weekend

m ex 5 · Post by **m ex 5** » Thu Jul 20, 2006 12:03 pm

I've started a new subject for discussing MX5 buying tips - find it here:
http://www.mx5forum.co.nz/viewtopic.php?p=12360#12360

Karl.

thanks for the link Karl

SLYDIT · Post by **SLYDIT** » Thu Jul 20, 2006 2:33 pm

when you replace the cambelt, get the tensioner pulley,water pump and front oil seal replaced also, while the mechanic has everything off. If youre water pump fails(and they do) you have to remove cambelt etc so no point paying for job twice!

Post by **simple** » Thu Jul 20, 2006 4:00 pm

Since it's an '89, if you're replacing cambelt etc. it would be prudent to replace the crank nose bolt with a new one (they cost about $17+GST, I think), and maybe consider loctiting it all up as a precautionary measure against the dreaded crank-nose failure! The bolts do stretch with time and re-using them is not the best plan, apparently.
Relevant info amongst here http://www.miata.net/garage/crankshaft.html and http://www.miata.net/garage/hsue/LoctiteCrank1.html

m ex 5 · Post by **m ex 5** » Thu Jul 20, 2006 5:39 pm

great tips., thanks guys, looks like i wont be getting that MX5 afterall, as we couldnt agree on a fair price

ahh well, the search continues, were not in any great rush, this one looked OK and was local, so bit of a shame, but the right one will come along!

m ex 5 · Post by **m ex 5** » Sun Jul 23, 2006 9:15 am

sadly the seller and I could not agree on a fair price, personally I think she didnt want to lose her baby and cant say I blame her for that........ so now I have found another one (as in own)

99 roadster

Shermio · Post by **Shermio** » Sun Jul 23, 2006 8:47 pm

m ex 5 wrote:sadly the seller and I could not agree on a fair price, personally I think she didnt want to lose her baby and cant say I blame her for that........ so now I have found another one (as in own) 99 roadster

Hmmm you have a Titanium grey 99? Was it a respray? it looks great from the photo in your sig...

m ex 5 · Post by **m ex 5** » Sun Jul 23, 2006 9:04 pm

Shermio wrote:
m ex 5 wrote:sadly the seller and I could not agree on a fair price, personally I think she didnt want to lose her baby and cant say I blame her for that........ so now I have found another one (as in own) 99 roadster
Hmmm you have a Titanium grey 99? Was it a respray? it looks great from the photo in your sig...

Hi yes it is and thanks, was done by the previous owner, I went over it with a fine tooth comb prior to purchase thinging the respray was for all the wrong reasons and hiding something nasty, but was convinced he simply didnt like the original orange.... not my favourite colour either I would have to say, but this looks great