[rich weyand]

I changed mine on an SBC, where the sending unit is between #1 and #3 on the underside of the head, and I hardly lost any coolant. Maybe a quarter of a cup, if that. More like an eighth. If yours is on the top of the manifold, you won't lose anything.

Here's what I did on my sbc. Put a pan on the floor under the sending unit. Have the new one standing by with just a bit of teflon paste on the threads. Yeah, yeah, I know, some people will tell you not to use any because it will insulate the unit electrically. Nonsense. Back the old one out until it is just about to come off. Now, holding the new unit in your right hand, spin the old one out with your left hand, and then with your right hand spin the new one in. If it is sticking out sideways like on the sbc, it will go glug-glug-glug-glug when you pull the old one out, but as long as the system is cold (not under pressure) it leaks out pretty slowly and it's only unplugged for a second or two.

I don't think you even have to burp it. I didn't. The coolant system is designed to clear the occasional air bubble. It will blow it out into the reservoir when it heats up and suck coolant back to replace it when the system cools.

But your gauge will never read right without the correct sending unit. And the Autowire #01513321 unit is the only one that I know is correct.