OK,
Full disclosure.
I was chasing a slight weep at the Left rear of the engine on the white 02 "Bolt".....
As I still do not have my full tool set to do head gaskets as they are still in Hawaii due to the virus related lock downs and quarantines, and
the fact that I needed to shift about 600 miles North with all of the kit, and needed to use Bolt to tow with.....
And, as Bolt has 156k miles on the clock, and has been a perfect performer in all other ways......
I very timidly added 1/2 of the small blue bottle of K-Seal to the rad tank....I know: Imminent disaster!!! Overheating, plugged heater core, ruined radiator...Etc....Ad Nauseum....
But wait! The weep stopped!......Then it returned a week later but much less....So I added the second 2 oz of K-seal (The other 1/2 bottle)
I have now done 2 major round trips 1400 mi each, and towing heavy trailers up and down the mountains
on I-5 and doing 75-90 mph in 100+ degree heat with A/C blasting with not a drop of coolant spilled, and no overheating issues!
I was, and am still fully prepared to replace both the heater core (with Audi) and the rad, which is factory......
However, as it is not blocked, and has performed much better than I expected on the towing trips, I will say:
"The stuff seems to work as advertised"
I will admit to being very surprised and expect to find a deep smouldering crater in my parking space sometime soon, but until then,
I am content to let things simmer along as they are.
I felt I needed to post this as the various snake oil quick fix "Mechanic inna bottle" type things seem to get nothing but bad reviews.
Could be I got lucky? Heck, I will take luck any way I can!
Oh, I am sure that some of the stuff will really ruin a cooling system, but hey! Just saying......
Cheers!

Yes, K Seal can be quite an emotive topic Bolt.... but it can also work, at least for a time on small/er leaks.(depending on just where they are in the cooling system)

The 'Active Ingredient' is Sodium Silicate (qv), in solution of course, which hardens to a ceramic-type substance if/when in contact with air and hot enough.

However I am skeptical of the additional materials some variants deploy, eg copper filaments & etc though - and certainly any water-course-blocking 'gloops' some of them use....

Hope it holds out for you; !

I know....this kind of thread is definitely "Poking the bear"
I agree about some of the chemical soups out there. I looked long and hard for the least aggressive product.
Since this one comes in a bottle that is only 4 oz., and is very thin in viscosity, it seemed the least likely to deliver unintended detrimental side effects.....so far, so good.
I WILL report any unintended consequences.
Frequently, these products are used by folks looking to flog off a vehicle with a serious problem and they do not care what happens later.
As I fully intend keeping this one, I went with caution, and for my particular issue, it worked....for now anyway.
With a bit of hope, I look forward to getting my shop set up here (I get to build a new shed! I am thinking heated floor....)
And getting my full set of tools over from storage in Hawaii. Then, I can do a proper head job, and probably a new rad as well.

The worst thing to do with it is try using it to fix a leaky water pump. Not p38s, but I've seen one seize solid and snap the pulley off it on a bmw after a neighbour of mine used it. Did stop the leak for a while. And I've seen a td5 with overpressurising coolant on a disco 2 where it seemed several bottles of it had been used to try and cover up various leaks, including water pump, head gasket and the oil cooler o rings. Wasn't obvious the pump was leaking until pressure was behind it. Radiator was noticeably blocked up with the stuff too. No way it was only a single bottle in there either.

He must have (also) used the aformentioned "pancake mix" type then Brian !?

Definitely lots of 'snake oil' variants available, with fanciful names like 'Liquid Copper'..... and it is expensive too..
whereas 'pure' Sodium Silicate (33%) solution is about a tenner a litre...

That disco looked like it had been fed a mixture if everything they could find. Definitely k seal in there as you could see the gritty bits but other stuff also possible.

Not sure which of the products the BMW got but same gritty looks to it.

Ok since the cats out of the bag. I had my P38 for a year and a half and every time I turned around something else went wrong. Then suddenly there was a coolant leak from the aft end of the left head. I couldn't bring myself to do a HG job after doing nothing but repair the vehicle continually. I put in a bottle of K-seal. The leak hasn't come back. The radiator hasn't plugged yet. I frequently drive the steepest highways in the country, at as warm as 35°C, with the temp needle staying in the centre. Incidentally, I've had the P38 another year and a half, and it's been very reliable ever since.

K-Seal will work on some leaks while others need Steel Seal (or plain ordinary Sodium Silicate, Steel Seal without a dye in it), it just depends on where the leak is. They are the only two I would consider using but the downside with K-Seal is the tell tale copper residue on the underside of the coolant cap. A dead giveaway if you are sell a car.......

I put pure sodium silicate in mine and it completely sorted the water getting into #6. Presume there is a crack behind the liner as there are no water galleries around that pot... lasted over 18 months with hard driving before pulling the engine to do the m57 conversion.

When I pull the head off at some point I will investigate.

I used steel seal in a M62 V8..

This came out the rad.

Like turkish delight

.

i think most people have used some type of sealant at some point in life for what ever reason , i don't recommend it but that doesn't help when your miles from nowhere. if you do use it go for the silca one as it does not tend to clog every thing or just sit their like a lump of crap. the visual appearance of the silica is a white powder on the internal surface . it usually lasts around 12 to 18 months as an average , that's when it works that is and yes i have used it more than once . just remember its a temporary fix and you still have to repair it ?

Copper?
Possibly there are more than one version of "K-Seal"......The one I used was in a very small blue bottle, and was not lumpy or gritty.......Kind of thin, beige and sludgy.....The orange coolant in my new reservoir (Nicely translucent) is nice and clear, not at all cloudy as I would expect?
No way there were enough solids of any sort to produce the "Turkish Delight" effect.
Actually, the stuff shown in your photo looks more like mineral precipitate from using very hard water for a long time!
Either that, or someone sold you calcium carbonate instead of Sodium silicate??
As I said, I will do an HG job when I get the tools here. Should be instructive.
Meanwhile, It's all good

The K-Seal we get here (but made in USA) comes in an 8 fl oz blue plastic bottle and has a coppery colour. According to their website, it has fibres that block the hole and tiny copper particles to fill the gaps between the fibres. It is usually that which can be seen in the header tank looking like it has been sprayed with copper coloured metalflake paint.

Not sure what SR had in his radiator, or how much Steel Seal had been used. Sodium Silicate usually just makes the coolant slightly cloudy and if any is spilled anywhere it dries as a whitish powder. Never seen it solidify like that, although there are warnings that it isn't compatible with OAT anti-freeze, only Ethylene Glycol, so maybe it was mixed with something it shouldn't be mixed with?