Is this product suitable fur use with cylinder head gaskets/

No. you shouldn't use this on cylinder head gaskets. As another answer says it's fine for sealing joints where there is oil and water. There should be no need for this product on cylinder heads.

Is this suitable to use for sealing oil sumps where a gasket is not used?

Yes, as per other questions. It's fairly rare that a sump won't have a gasket - it may be useful to double check on that, if there are any online resources available on the engine in question. You could also look at making your own - from gasket paper. Still use Hyl/similar, but that might be my preferred option unless specific manual informs otherwise

Would this be suitable for a taper thread union on a petrol line?

My opinion is that it should work but a taper thread may seal better with PTFE tape, (Plumbers tape)

can it be used to seal outlet on woodburner

Hylomar Universal Blue has an operating range of -60 to +600 degrees farenheit. If your woodburner's outlet is less than 600f, then you can probably use it. If it's just below 600f, I'd think twice about using it, as it may start to give off toxic fumes. Why don't you use the proper stuff, ie fire putty/cement?

ASIN	B0064M6A6G
Best Sellers Rank	2,579 in Automotive ( See Top 100 in Automotive ) 40 in Fillers, Adhesives & Sealants
Brand	Phixnozar
Customer Reviews	4.7 4.7 out of 5 stars (311)
Date First Available	30 Mar. 2011
Delivery information	We cannot deliver certain products outside mainland UK ( Details ). We will only be able to confirm if this product can be delivered to your chosen address when you enter your delivery address at checkout.
Item Weight	50 g
Item model number	F/HMMS00C/040G
Manufacturer	Hylomar Ltd.
Manufacturer part number	HB40G
Model	F/HMMS00C/040G
Package Dimensions	13.11 x 3.3 x 2.59 cm; 50 g

Hylomar F/HMMS00C/040G 40g Universal Blue

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