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Oil Pressure Relief Valve - Is It Repairable In-Situ?

4K views 8 replies 5 participants last post by  miles 
#1 · (Edited by Moderator)
TL;DR version:

Has anyone repaired or replaced their oil pressure relief valve?

Can the work be done with the sump pan taken off and the oil pump (and whole engine) still in place??

The Long Version:

I have an early 1.6 (SNC) engine and 'real' oil pressure guage, and it currently shows super-low oil pressure most days - somewhere between 0.25 and 0.5 bar on hot idle, maybe 2 bar on cruise under load, rising to perhaps 2.5 or 3 bar when giving it the beans. Even when there's ice on the ground in the morning, it struggles to reach 4 bar on initial start-up.

It's got to the point that I sit in traffic raising the revs to get 'idle' to about 1500rpm and the pressure to rise to about 1bar, 'just in case'.

However, there is the odd occasion when it will happily sit at 1 bar on <1k rpm idle and rise to 4 bar under load - but they are few and far between and there is no easily identifiable pattern to it... :rolleyes:

@punchdrunk says in this thread that pressure at idle doesn't really matter:
http://www.mx5nutz.com/forum/index.php?showtopic=27137&hl=%26quot%3Boil+pressure+relief+valve%26quot%3B#entry385678
but others disagree with him.

Either way, I would like to try and see if there's anything I can do about it.

From reading around the forum and the wider internet, it appears that the problem could be one of a few things:

-- a faulty oil pressure sender (£100+ from MX5Parts),
-- dodgy connections to the current oil pressure sender,
-- it might need a service and a replacement oil filter - OEM or equivalent quality (although a service last year didn't fix it the issue, perhaps improving it by half a bar of pressure),
-- or... the oil pressure relief valve is malfunctioning, which seems to be mentioned quite often on here as a possible/probable cause of low oil pressure (but no-one really posts back with their diagnoses after asking questions about it, or the fix is an engine swap!).

I can try cleaning the connections to the oil pressure sensor to see if it is just that, which would be a nice cheap fix, but I have previously had issues with tappets getting noisier and noisier when sitting crawling along in gridlocked London traffic in 25degree+ weather for a couple of hours - which makes me think it might genuinely be low oil pressure, as mentioned on the following link (although it could just be the oil struggling to cope with the excessive heat, as I've not really noticed it since):
http://www.mx5nutz.com/forum/index.php?showtopic=41272#entry557317

I do want to get it serviced, so can cover off the third aspect easily and cheaply enough, but if it is the relief valve, it seems that either an O-ring may have failed, meaning it won't hold pressure regardless of what the spring is doing AIUI, or perhaps the spring is stuck partially open.

From what I can tell from the mellens online manual diagram, the oil pressure relief valve is part of the oil pump assembly, which looks to be confirmed in the other manual pages in this blog that I found:
http://blog.miataracer.com/2014/04/everything-you-never-wanted-to-know.html

and the thread that blog took the photos from also shows 'sump off' pictures of the oil pump in-situ, with the relief valve visible:
https://forum.miata.net/vb/showpost.php?p=6542137&postcount=8
(middle right of the 'pan off' picture and I think?? top left of the zoomed in pic of the half-moon gasket)





(Can taking the sump off even be done without taking the engine out? @NickCann says here that it's an engine out job but I have also read somewhere it might be possible to drop the subframe?:
http://www.mx5nutz.com/forum/index.php?showtopic=150527#entry1777888)

The sump-off pics would appear to show that the relief valve is visible with the sump off, but it's not clear if the valve/spring mechanism is accessible / repairable with the oil pump still in place.

@Horton says here that one cannot check it without removing the oil pump, I think? Is that correct?
http://www.mx5nutz.com/forum/index.php?showtopic=150386#entry1774109

Or is it possible to remove/refit the spring mechanism without touching the oil pump unit??

The exploding diagram in the blog linked to earlier seems to suggest that by removing the cotter pin(?) marked as 99221-3035, one can access/remove/service/replace parts 14-115, 14-116 and 14-118, which would seem to make up the relief valve assembly:
http://2.bp.blogspot.com/-bDgCrE6IIVw/U0Wo-tM4VQI/AAAAAAAABgI/sbOItsJFH0Q/s1600/94oilpump.gif

If it is possible, it looks like the spring length should be 45,94mm:
http://mazdaracers.com/topic/5538-oil-pump-question/
but the picture guide detailing the measuring process completely skips the steps between pump removal and spring inspection... :rolleyes:

It's not clear, however, if @andyone means that the standard oil pump allen screw needs sealing or just one on a replacement boundary pump?
http://www.mx5nutz.com/forum/index.php?showtopic=102476&page=7#entry1420465

That is all a lot of work, though, so @Mozza has suggested that one easy alternative option mught be to try to dislodge a stuck spring using compressed air?:
http://www.mx5nutz.com/forum/index.php?showtopic=179994#entry2135402

If anyone is able to offer any thoughts, guidance, advice or real-life experience, it would be much appreciated!

Many thanks in advance for any input!
 
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#2 ·
Swap the gauge for a light. Then you will be happy. As its only a reading your concerned about.

Rattling top end in mid summer jams (at the drive through) have been the norm for all 3 of my engines. Likewise low pressure readings that can't possibly be true, when just above freezing. I think most people just keep this sort of thing to themselves, like turbo play and leaky weather seals. I have a second sender to fit, but whatever? The top sounds fine after a quick rev, to replace the stinking hot oil that the tappets couldn't hold. It's no mystery. The bottoms have never shown sign of issue, except the reading, that I can plot out for any weather conditions. Having done the 12 month cycle about 12 times, I know it means nothing. Though it does explain why the later cars get a light, not a gauge.

I wouldn't start stripping the car. I would look at better measurement methods. I might post some later, but my pc can't keep up with my typing as usual... Making posts very time consuming
 
#5 · (Edited by Moderator)
Thanks for the replies, chaps :)

Working on the basis of easiest and cheapest first, I got my hands dirty (!) and checked how well the connector was fitted on the oil pressure sensor.

It seemed fine and I couldn't get it off to actually clean it, but it now seems that my oil pressure is within the normal range (about 1.5-1.75 bar at warm idle, 3.5-4 bar when under load and driving) so perhaps it was just a bit loose!

Will keep an eye on it and if it drops again, I'll wiggle the connector and see if it fixes it again.

This is the sort of fix that I like - free and easy to do... :D lol

Mind you, after so long with it being so low, I've got used to the lower readings, so glancing down and seeing 4 bar now makes me momentarily panic that it's going to go pop! LoL
 
#7 ·
This is why Mazda fitted the idiot gauges (and presumably other makes just fit lights). No point giving people information they just worry about it.
 
#9 · (Edited by Moderator)
Take the bulb out. Happy days.

Mazda actually did change to fake gauge as they were inundated with customers wanting their perfectly fine cars fixed under warranty because the gauge kept moving.
 
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