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MG Midget and Sprite Technical - Blanking plug

I am using a 1098 engine with the head having a tapped hole to take the temperature sender. Only its in my car with a MK1 vertical flow rad which uses the temp sender in the header tank. So I need to fit a blanking plug in the hole in the head.

Can someone tell me what the thread size for that would be. None of the contents of my mis-named "useful bolts" tub fit.
GuyW

Minispares sells them for £3.30 incl Vat. They are quite common so you may find one S/H. part number ADP210
Bob Beaumont

Thanks Bob.
Walking encyclopaedia. You always know the numbers.
But I suspect you have a secret list
GuyW

Guy
I have the same situation (with the 1275) which I realised only today. I wondered whether the temp sender would be better in the radiator or the head? It's the same thread.
Bill Bretherton

The temperature reading will be much more consistent taken from the port in the head than from the radiator.

I had a 1098 midget (1965) and the temperature gauge made wide swings when load changed due to radiator porting.

I much prefer the gauge stability (and veracity) in the 1971 Midget.
Glenn Mallory

Either way, I need to blank one of them off. But if they are the same thread I can decide which one later. Only I am not sure that the sensors are the same,or at least I don't think the rad bulb probe would fit into the head, it's too long.
GuyW

I've got my Frog sender attached to the head of my 1275. The radiator is plugged with an old bulb and retainer. There was probably a reason that they moved the location to the head from the radiator, probably for what Glenn says.

Edit: I don't have any interference of the bulb with anything internal in the heard although my gauge isn't original to the car. It was replaced at some time and the bulb may be shorter.
Martin

To fit the capillary bulb in the head I think you need this adapter to stop the bulb hitting the inside of the head https://www.ebay.co.uk/itm/Smiths-Water-Temperature-Gauge-Bulb-Adaptor-11K2846-for-MGA-Triumph-2000-TR-/201787045163 .
David Billington

David,

That looks like what came on the two heads that I have. I know that I never had to do anything other than screw the bulb and retainer in. Of course these are US market heads so something might be different. We all know how BMC/BL changed things around.

The bottom picture on page 100 of Horler shows what I have for a connection to the head but I do have the original Frogeye radiator and I don't know what the 1098 had so you are probably correct about the adapter.
Martin

Temperature gauge bulb in the head's best, if the thermostat happens to stick shut and the engine gets hot it won't show up with the bulb mounted in the radiator tank till it's too late
William Revit

I believe that the adapter would indeed be required. My 1275 came with one. On the other hand, there is no harm in removing the plug from the head and giving it a try. If it fits, wear it.
Glenn Mallory

My plumber shop sold me the right hardware. It is quite common and cheap stuff (here on the continent)...

Flip
Flip Brühl

Guy

I wish you'd mentioned it earlier. I've got lots of those adapters.

What were you saying about keeping things?
Dave O'Neill 2

This is interesting. The 1098 CG engine my Frogeye came with has no drilling for the sensor. Must only be 1098 CC and 1275. So I presume the plug Bob refers to can be screwed into the head or the older radiator depending on where one wants the sensor.
Bill Bretherton

Dave "my friend" only discovered ( or rather, remembered) that he had a hole in his head when, on filling the cooling system, he heard a gentle trickling sound.

More investigating and rummaging in useful bits boxes required this morning.
GuyW

The thread in rad top and the 1098 head is the same, so the double ended male threaded adapter does relocate into the head. At first I thought the sensor probe wasn't going to go fully in but a bit of wiggling and it has seated correctly.
I now have to find a plug for the rad.

How long does it take to fill a Frogeye cooling system? Oh, about a week!


GuyW

A copper washer goes with the adapter.

As on the last two installations I've had a leak with the bulb and adapter (sorted with red Hypotite 100) I recently bought a new adapter and copper washer but I've yet to do the job that will require them but I wonder if the new adapter will sort the problem or even make it worse.

A trick I read recently, put some (forget what) into the adapter after fitting the tube (petroleum jelly? - silicone grease?) so that it melts with use and wicks in to make removal easier if required.
Nigel Atkins

Guy

What type of gauge do you have?

I'm not sure about Frogs, but the later gauges have a male tube nut, whereas yours appears to be female.

Nigel

I always put a couple of turns of PTFE tape around the sealing face of the bulb, where it contacts the adapter seat.
Dave O'Neill 2

The adapter is double ended male, so screws in and presents a thread for the brass female nut on the sender.

I usually use PTFE tape buy this time used a sealing paste from a tin an engineer gave me around 40 years ago. It's like a very thick green grease, never dries out and is very effective on hot surfaces
GuyW

(ETA: I'm too late again, I was trying to find the thread sizes but couldn't.
I always worry about using PTFE on non-threaded opening - and sometimes threaded.)

(PS - would the PTFE on the bulb make the gauge more accurate?)

I didn't see Guy's last post or photo when I posted and I can,t see any washer used (the plug Bob mention uses a fibre washer).

To save necks and eyes (and remove distracting non-original trunking) see below.


Nigel Atkins

Well I have no fibre washers of the exact size required so I used my green goo instead. It has never failed me yet for this type of application, but only time will tell.
GuyW

Ah, I see, and I think I see why that part of the photo might appear a bit blurred to my eyes, it might be the green goo.

So you painted the engine to matching the sealing goo, thrifty beyond call.
Nigel Atkins

Guy,

As Dave asked, what kind of gauge do you have? My Frog has the original (albeit replacement) gauge on which the treaded nut that goes into the radiator is male which is also the same as the later cars that go into the head. Curiouser and curiouser. Obviously, you'll get concourse points off for that.
Martin

Martin, I'm not sure that original and replacement sit well together in the same description!

My Frogeye rad has a female threaded boss which would take the later style sensor with the captive male threaded tube nut (as your replacement item). Or take the double ended male adaptor to receive the original sensor probe and brass female retaining nut. Because the early style probe fits into an adaptor the bulb is slightly longer than the later version and this could be why it may snag on the casting when used directly in the head. Mine didn't.
GuyW

And, in my search for a plug for the radiator, now that I have, by popular demand, moved the sensor to the head, I have found at least two alternative solutions. The blanking plug in a standard inlet manifold is exactly the same. Only for now I need that to stay where it is. But in my maligned useful parts box (all is forgiven) I found a discarded electric sensor (ex 1500 midget c 1995 perhaps). I don't know if it works, but it is the right thread and size to close off that rad boss.
GuyW

Guy,

Glad to see that you've sorted things. When I replaced my original gauge, it was because the sealed line had broken and I made sure that what I got was the same as what I was removing which goes into the female radiator treaded boss. As a matter of fact, when I installed the bulb into my 1275 head, I used the old bulb and male retaining nut to plug the opening in the radiator. And even though I've replaced the radiator, I'm still using the original 1959 bulb and nut.

All of which raises the question, when did BMC change over. My Frog was originally built in April 1959.
Martin

Martin, from what we have, I don't think it is as simple as a single change over date. Mine is a later car (1960 build date) but has what I took to be an earlier variety, being the brass female nut fitting. Bearing in mind that these were bought in by BMC I think it is likely that they accepted both versions, at least for the MK1 cars.
It's a simple enough to supply the female nut version with the male/male insert adapter in which case it can be used either in the rad top (MK1 Sprite) or in the head ( 1098/1275 engines. Though in production I suspect the ones fitted to the head were usually the direct male fitting, as yours.
GuyW

So what you're saying is that this is just one of those BMC mysteries? What's in the parts bin today?
Martin

This thread was discussed between 25/06/2020 and 29/06/2020

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