Question about coolant hoses from engine to water heater

[leecea]

I have a Yanmar 3GM30F with coolant hoses running to a water heater. I have a couple of questions and have attached pictures below.

1) What is the grey plastic knob like thing inserted into one of the coolant lines?

2) The coolant lines are hose clamped to a threaded fixture. That seems worrying to me. Is it common to do this? If I undo the clamps and pull the line off will it get damaged so I can't re-use it?

Thanks,
Andy

[Bowdrie]

I surmise that the "gray plastic knob" is simply a cap that you can unscrew to add coolant, and also to vent air from the loop that feeds the water heater.
Due to various schemes of water heater mounting it's not unusual for them to have "air locks" which compromise, or even inhibit the coolant flow.
Perhaps the threads on that fitting end shortly after entering the hose?
Only one way to find out, agree, hoses clamped over threads are seldom satisfactory long term.

[leecea]

Thanks - it makes sense about the knobby thing. That's might be pretty helpful.

[glenn.225]

The Knoby thing as you called it, was/is very commonly available as part of an automotive rad flush kit. And as noted is very handy for venting air from coolant hoses. The thread on the vent is same as your garden hose, so if you need to vent the system you can attach a appropriate length of hose.

The fittings are not threaded rather they are hose barbs. Yes you can remove and reinstall the hoses (sometimes), if they have been on there a long while they may actually have to be cut off. Usually by twisting and pulling forcefully they will come off.

By the way this does look like a good installation, double hose clamps [emoji106].

[kmacdonald]

I don't know why they double clamped in some places. Single clamps are fine. You only need to double clamp exhaust hose lines. The knob is a vent (or flush kit) and probably isnt needed. If the water heater is higher than the engine it might be needed.

You can reuse the hose if you can get it off without cutting. Twist it and it will usually break free and turn. Then try pushing the hose off, not pulling it off. Pulling it tends to tighten it around the hose barb. If there is enough hose cut a couple inches off before reusing. Looks like a decent install so dont mess with it if there isnt a problem.

[stormalong]

Double hose clamps are used for insurance. However, if the barbed fitting is too short for two hose clamp the second clamp is just crushing the hose.

Speaking of crushing the hose the pictures show just that. Especially the first clamp in the first picture. The hose clamps are too tight, deforming the hoses. Also the hose clamps that have the straps cut through for the tightening screw are much weaker than the type where the threads are formed in the strap without cutting through. That, combined with over torquing the clamps is how they break. Once crushed like in the picture the hose strength is compromised. If you have to remove those hoses replace them.