91 van had a
head gasket leak 2 yrs. ago. Used KW block sealer- worked great. Today, the temp
was erratic- didn't overheat, but seems
to be using some water (not leaking).
Have to drive it tomorrow and I bought some
Bar's Block Sealer. Any chance it would not be
compatible w/ the KW stuff and make things worse?
Please don't tell me to pull the heads and do it right- not an option and the Block
Sealers often work- I know from my experience and others.

if it's using water and you don't have a leak, where do you think it's going?
for block leaks, the Moroso ceramic seal has alway's worked for me if you follow the directions.
if it's a head gasket, well, pull the heads.