Temperature gauge adventure

[Rabbitt]

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Something supposed to be simple , but maybe it isnt. A bit of a rabbit hole
I have a 1957 803cc series II Positive Earth here in NZ.
1 : Have done my homework in the forums but probably only got a D- mark. Definitively , will a Smiths Temp gauge operate in a positive earth car. appears that the answer is NO ! I do have a voltage regulator but that overall option seems a dead duck.
2. So I have bought a mechanical gauge as suggested but of course there is no engine block source to tap into , therefore a radiator hose adaptor is required , which I have also purchased.
3. A couple of difficulties ... the sender bulb is too large for the adaptor insert hole tap (NTP) and most of these adaptors have a default thread size.
Also , even if the insert thread was correct for the sender bulb and it was possible to screw home , the end of the bulb would bottom out against the other sidewall of the adaptor itself. (even if the supplied thread adaptor is used giving more length.) So the sender is both too wide and too long !
Any ideas ?

[philthehill]

Get the right adapter !!.
If your hose internal dia is 25mm as I suspect it is having just measured a Minor top hose then this is the adapter you need with the 5/8" UNF thread.
https://www.merlinmotorsport.co.uk/p/25 ... aptor-ha25

You may need one of these to space the transmitter way from the hose adapter.
https://www.moss-europe.co.uk/adaptor-t ... -3-11k2846

[Rabbitt]

Thanks .. searched all over for 5/8 thread sensor sizes on hose adapters Ebay/Aliex/Temu and locally ... and all were default 1/8 NPT.
So this link is the first I have seen and will likely suit ... I will recaliper the hose internal again as I thought it was smaller. Cheers

[Rabbitt]

I’ve had another look around the forum and eventually found several replies on the same subject. very helpful. I actually have two hose adapters and have decided to tap out one of the sensor threads to a suitable size plus an adapter.
I managed to get a different gauge and sensor whereby the sensor was thin enough to fit through a 1/4 npt entry which will all work.
continuing to fit this to the top hose position i’ve now discovered that to get the adapter plus new hose sections at each end is a pain to insert and fit between the radiator and thermostat housing even with heating the two hose pieces to be flexible enough. There is not enough room to flex and manipulate properly. I may have to consider draining and moving the radiator left slightly to do this.Some of the forum discussions have asked questions about repositioning the adapter somewhere else such as the engine water tap or else elsewhere.
Quite correctly one member said that although some positions may not provide a definitive reading the main point is to establish a consistent reading. So, on that basis replacement in the bottom hose be okay? I realise that reading might be not correct but at least would establish median. The bottom hose is far easier. Are there any tricks with inserting into the top hose position that would make the problem easier?

[Bill_qaz]

Not familiar with 803 engine but could you use the thermostat housing that has temp sender appature, like this?

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[svenedin]

My Minor is also positive earth and I did toy with the idea of fitting a water temperature gauge and an oil pressure gauge. I rather like the Smiths gauges that combine this in one instrument. I e-mailed the technical department of Caerbont Automotive Instruments and they told me that their modern electronic gauges are only negative earth but they said "the old bimetal gauges are just resistive inside" and so can be run either polarity but must use a voltage stabiliser. Of course purely mechanical gauges do not care about the polarity. Anyway, I never got as far as asking them what they meant by the old bimetal gauges as I decided I really don't need extra gauges. 37 years with my car (a 1098cc) and I have managed without worry gauges for this long.......

If I really wanted extra gauges then for simplicity's sake I would just change to negative earth but I'm not going to do that!

Stephen

[MinorOCD]

Re. Fitting the sender in the bottom hose, this will not work as you will be measuring the temperature of the water that has been cooled by the radiator and will be of no help if the engine is overheating.
The solution Bill suggested, in the thermostat housing, is the best one. I have (on a different classic) fitted and electric water pump that needs a fairly accurate reading to operate correctly.
I used an infrared thermometer to measure various parts of the engine and cooling system and there is a marked difference comparing various locations. The radiator is always a lot cooler than the engine. The thermostat housing, because it’s bolted to the head and filled with water from the head, is the most accurate place. It’s also easy to fit the sender.
In my case, I bought an aluminium threaded boss to match the sender and Tig welded it in. You could take it to a local welding shop to have this done. You can buy these threaded bosses from Merlin Motorsport and similar places. With luck, the item Bill found might be a bolt on solution.
All the best,
Paul

[Rabbitt]

Thanks for your input , yes agree , the only gauge I would consider from my perspective is water temp. Not bothered about anything else.
I guess over the years I have always been overly careful even on our newer cars with monitoring temperature. I have inadvertently overcooked a couple and been caught due to one in particular having no actual gauge, only a dash illumination light.
Considering resulting expense, a $50 option makes sense. I'm OK with the single oil light within the Speedo on my Minor ....
A major 803 motor issue here in NZ would be an uphill battle..
I reckon by draining and moving the radiator left slightly I can maneuver each of the hose ends over both Rad and Thermostat ports. Probably fit the Rad end on first - then on the thermo...soften the hose and use a little drylube or similar. Looks like there will be room to wiggle.
Cheers

[oliver90owner]

The “idiot’ light (as we call them), for oil pressure monitoring, is often simply too late to save the engine from serious damage. Water temperature indication can also avoid costly repairs.

Modern alternators rarely fail but can result in battery failure, so some charging indication (ammeter or voltmeter) is good although the ignition light, at start-up is usually a good indication the system is working. Of course, with a dynamo fitted the drain can easily exceed the charge rate - that is where an ammeter comes in handy.

It is just a matter of balancing the cost of indicators (if they actually get used) versus the likely cost of an engine failure, etc.