The 'E' Type Forum

Went to remove the water temp sender to replace it today and it's stripped the threads (Series 1 4.2 part number C16895)

What are my options? Can it be helicoiled, and if so what size?

Thanks!

5/8 unf 18 is the sender thread..so a helicoil or adaptor to suite....Steve

Thanks. I've never used one before, but I guess restoring an old car it was inevitable...

Another question - what sealant should I use on the helicoil to prevent any leaks?

There are other thread repair inserts other than Helicoil...I havent used one in this location....possibly a Timesert could be a better option....others may chip in with ideas...Steve

I would be inclined to use a Timesert repair here as it's a solid threaded sleeve that should be easier to get a good seal to the aluminum manifold using most any type of liquid sealant.

Oof! Just checked the cost of time sert kits! About half the cost of a new manifold!

I might give v-coils a try first with some permatex high-temp sealant on both sides...

Had the same problem with my 3.8. I noticed that there was still good thread below the reach of the sender unit. I just happened to have on my shelf a generic sender unit with a much deeper reach which fits tightly and works perfectly.

Knightrider wrote: ↑

Sat Jan 24, 2026 5:09 pm

Oof! Just checked the cost of time sert kits! About half the cost of a new manifold!

I might give v-coils a try first with some permatex high-temp sealant on both sides...

Take it to your local thread repair place.

We have Captain Thread and Doctor Bolt here.

A bit of a pain as I'd like to avoid removing the manifold if I can... And the car can't be driven.

However, you did get me thinking and there are a few mobile thread repair companies in the UK that I will give a try.

To me, the sealing compound is the last of your worries.

Any kind of « helicoil » will do the job, personally I would stick with that « wire » type rather than go even bigger in order to fit the solid-wall Timesert approach - the latter are much stronger, but this is an essentially no-load area.

The difficulty, with a capital D, is being able to bore out the hole to a bigger size with the manifold on the car.

Free-hand drilling a hole that big, getting it square to the face, and producing a round hole, to size, is beyond DIY skills.

And following it up by getting the tap to cut the helicoil thread true, and to size, is of a similar difficulty.

Both should be machined off the car, one after the other, using the same machining axis.

Or, find a longer sender, like Randall says.

True - I do wonder how you ensure that the drill-tap go straight when heli-coiling in situ. There are plenty of videos out there of people doing it successfully - given that the drill bit is only very marginally bigger than the existing hole I guess the drill/tap will centre quite easily?

The suggestion of a longer-thread sender might be a good one- I tried the original sender without the washer today (to allow it to screw in a bit further) and it did bite fairly firmly... I'll order something and see if I can get it to seal before I try anything more drastic. I am guessing that it will just throw up another issue of calibration - but if it seals the hold I can work around that for now!

How about counterboring the hole to allow the sensor to sit a little deeper? Maybe easier than fitting an insert.

Another good idea... I can't use the original sensor, so I will try a slightly longer replacement one first.

Effectively, if I can get it watertight I will be happy as it will allow me to run the engine....

All these suggestions are fine but Rory is spot on, as usual.

Why over-complicate the problem when replacing the offending helicoil with a like for like item is the easiest and least invasive means?

You can buy a helicoil extraction tool for around £20, which will remove the remaining part without any drama. Then for another £30 or £40 you can buy a helicoil insertion kit, with parts the correct size and the job is done. No drilling or machining required and no swarf in your manifold.

You might never use the tools again but it's cheaper and easier than stripping things down and sending them off for repair.

Regards

I think you misread - it hasn't previously been helicoiled - the original threads are stripped. So unfortunately not quite as simple as replacing the coil!

I find that surprising because it is normal practice to fit thread inserts in aluminium parts, especially cast parts. Even more so if the thread is being used to secure a replaceable item, such as a thermostat. It strengthens the thread and makes it much more durable.

Also, if galling or corrosion has occurred, it is quite common for the insert to come out with the part being removed, leaving an oversize threaded hole behind.

To answer another question, use a medium strength thread lock on the insert when/if you fit one.

Just trying to help make things a little less painful.

Regards

No fittings into the aluminium heads have inserts....every fitting is straight into the aluminium....spark plugs etc

OK - so the prize goes to Randall!

Picked up a generic marine sender from https://www.asap-supplies.com/products/ ... pt-ke00005 which has longer threads than the standard one:



This grips the remaining thread in the inlet manifold securely.

Before installing, I wanted to check the calibration with the gauge in the car, so rigged up a test circuit with some jump leads and a sous-vide cooker:



This shows that the sender is actually pretty much spot on from around 40-100 degrees C.

All installed, no leaks, engine up to temp with a working gauge. Thanks all for the suggestions.