Re: Tell-tail location

[Don]

Well, usually the telltale elbow is located in the exhaust manifold cooling jacket, which is the beginning of the cooling circuit in the powerhead. The problem here is that the original exhaust cover on your 72 50hp does not have a threaded hole for the elbow, or a boss on the cover suitable for drilling. You certainly could drill through the water jacket on top of the block, forward of the head gasket and install an elbow there. The problem is that you must be very careful drilling to avoid drilling through something you don’t intend to drill through.
No matter where you place the elbow, good water flow from the telltale does not guarantee the engine is cooling correctly. The three cylinder models have an elbow drilled through the top of the block in the exhaust cover/manifold cooling area, this helps ensure no air is trapped there.
Again, I want to emphasize you must be very careful where you drill, or you might make a terrible error. I guess the easiest way to figure out where you can drill safely is to have a donor/dead/damaged powerhead that you can pull the exhaust covers and head off. You can do test drillings on this piece instead of possibly damaging your powerhead.
Trying to drill through the cylinder head water cover in an attempt to put the telltale "after the thermostat" would be near impossible. The cover is very thin, and the passage in the head is very shallow.
No matter where you put the telltale, it is unlikely you will be watching it if the engine overheats suddenly at high speeds…I "think" your 72 50hp uses a hot horn, check this feature and make sure it is working properly. Simply turn the key on, separate the knife connector for the temp sender, then ground the powerhead end of the tan lead to the block, the horn should sound…..