Temperature and oil pressure gauges

[Trevor]

I would agree re oil preference....I have been a Castrol user (incl full synthetic)for many yrs in both road and competition cars.
I believe that 'quality' oil of the right viscosity, changed regularly is more important than actual brand.
In my tweaked naturally aspirated 1.8 I am using Castrol Magnatec on 5000k oil changes. I get some initial occasional lifter ticking as the oil approaches its 5000klife.
When I bought my car, the oil was black and hot pressure fluctuated with a lower than expected reading. From its very first oil change, pressure improved markedly and has never budged in the last 25,000k.

It would appear that you do not have the OEM oil gauge. Information as to your mod. would be of interest.

[zorruno]

It would appear that you do not have the OEM oil gauge. Information as to your mod. would be of interest.

I assume by that you mean oil gauges that just have 'pressure'/'no pressure' indication?

I'm not sure what model Ian has, but it wasn't until about '96 I think that 'binary' style oil gauges were fitted to MX5s. Most of the earlier models had reasonable 'analogue' oil gauges. Even though the earlier ones were supposed to be 'true' oil pressure gauges, I wouldn't count on their accuracy.

Rumour has it that the gauges were to avoid customer callbacks to the dealers in the US, and 'confusion from owners', as people were worried that the pressure was slightly different on their model compared to others, or changed slightly with temperature etc. The new senders may have been cheaper for Mazda too...

There are some 'howtos' around to change the 'binary' gauge to an 'analogue' one however for those who like to watch their oil pressure change.

cheers

[R LTD]

My understanding is that the pre 1991/2 MX5s had an oil gauge that recorded actual the pressure. The later 1.8 MX5s have a gauge that simply reflects pressure is ok similar to an oil pressure light. I presume this is what is meant by a binary gauge.

R Ltd

[Trevor]

Thanks,

I am aware of the situation and think Mazda should be taken to task, on the basis of deceiving buyers. The water temperature "gauge", I understand is the same on/off idiot light con.

I thought that a number eight wire Kiwi fix, may have been found, superior to the mods I have seen used elsewhere.

It is not that I am all that concerned, knowing exactly what indication is on, Tap, but this on a so called sports car. !!!!! ??????

[Ian]

I have a late 93 NZ new car with factory oil guage. I believe from past reading that these are not the most accurate, but on checking with the dealer's workshop manual, my reading is spot on (3000rpm in top gear, from memory)
Whatever, there was a marked increase in the indicated pressure/less fluctuation after the initial oil/filter change.

I don't attribute this necessarily to Castrol as such, but to having fresh oil and a clean filter....
Any oil which flows quickly from cold ie a 10-40 etc will help with the lifter noise in my view. Certainly I am an advocate of 5000k changes.....

Cheers, Ian

[zorruno]

My understanding is that the pre 1991/2 MX5s had an oil gauge that recorded actual the pressure. The later 1.8 MX5s have a gauge that simply reflects pressure is ok

My 94 Roadster records variable pressure. I suspect maybe the non-Japanese import MX-5 models may have switched to the simple gauge earlier.

[Trevor]

For the record, I should have included that mine is an 1800 5 speed, 1997 japanese import.

[Fletch]

In the USA, '90-'94 Miatas had the "real" oil pressure gauge, and '95+ had the "idiot" gauge...

I've seen nothing to suggest that the same change didnt happen at the same time for other markets (ie, NZ-new and Japanese imports).



The water temperature gauge is deffinitely NOT an on-off type operation...


It is non-linear. It has a "dead-spot" where its reading doesnt change....
When it reads low, your engine hasnt warmed up.
When it reads high, you need to do something (like stop the engine).
When it reads near the middle of its range, then its warmed up, but not dangerously hot, and its had its internals tweaked so that a RANGE of normal temps actually give the same static reading.

Some would prefer a more linear action, but this non-linear approach has its reasons, and is not completely stupid.

From experimentation, I can tell you...

the needle will stay pegged on cold below about 45 deg C
the needle will be up to normal by about 70-75 deg C
the needle will start to rise above normal at about 110 deg C.
I havent let my engine get hot enough to know how hot a full-scale reading is?

Fletch.

[SLYDIT]

If you search on Miata.net there is a thread on how to linearise the gauge so it reads like a t true linear temp gauge with no dead spot in the middle. it requires a few new resistors and a capacitor from memory.

[jif]

by the time it's pegged at "H" temp is 116 C + ... a friend of mine drove like this for a few more k's until he got to the service station and it's still OK , several years later. Cast iron blocks are great

The original question (back on topic) was about whether the oil was "synthetic" (marketing double-speak version) or real, actual synthetic - as normal people would understand it - ie coming out of a test-tube...

maybe it's best to just go with a known quantity (Amsoil, Motul, Mobil1 etc) when you have a turbo'd daily driver that runs hot ..!

http://www.amsoil.com/products/atm_test ... flash.aspx
http://www.worldsbestoil.ca/dyno-test.php

[Trevor]

Thanks all for the info on the temperature gauge. Now that I have this, it makes it more useful, rather than an ornament.

When I have time, I will post some interesting information regarding experience I have had with my cooling system.

Cheers< Trevor.

[zorruno]

I havent let my engine get hot enough to know how hot a full-scale reading is? Fletch.

I have...

It appears to be a physical limitation due to the right hand side of the gauge not letting the needle progress any further.... Luckily no long term damage to the engine....

[Grant]

Mine (1998 NB) appears to have a problem as well. When going up a long steep
hill quite slowly, the temperature gauge doesn't move from the normal
condition, the radiator fan doesn't come on, but if I stop then it's obvious
the water temperature has risen as it's gently boiling! Can't hear it from
within the car though (roof down of course) so only notised the first time
when I saw water coming out the overflow.
Any ideas?
The fan tests ok, it appears to be a problem with a temperature sensor or
control of the fan somehow.
Grant.

[Trevor]

Greetings grant,

Coolant should not be coming out of the overflow and should be retained in the container. Refer to my separate thread, as you may have the same problem as I had and found a fix.

Cheers, Trevor.

[KSCRIM]

I have done the linearization mod on my NB. It works and I can see when the thermostat opens by the slight drop in reading.
Fletch is right, there is a flat spot from 160F to 225F and the end of scale (=H) is about 250F
PM me if you would like the info. It is fairly easy to do, but some soldering skill and care is required.
Edit, attached the info. There are 2 files and it seems I can only attach 1, I'll post the other.

[KSCRIM]

Here is the other file, the descriptive one. If it dosn't appear, PM me with an email address and I'll send the files that way.

[Grant]

Thanks for that. Will have to do the mod now and see how it works out.