Did you get the heater hoses from HPS too? Thought I saw a kit from them but pic did not seem to have them molded the same as a factory set, or maybe I looked wrong.

 

I've bought heater hoses in bulk from diesel truck repair places. I believe the ones you see on my Jeep came from eBay. Just so you know, the In / Out on the heater core are slightly different sized. Obviously, the larger sized will have to be coaxed on. I think I used a little bit of soap to help it slide on.

 

I was looking at that size issue too. On breather lines what I've done, and am about to do some more, is match the large diameter for a snug fit. Then, on the smaller diameter part I out some heat shrink tube on the nipple to fatten it up enough for the hose.

However, I am hesitant to try that with a pressured line of any kind especially one with great temp swings like a coolant/heater line. Not a fan of stretching it onto a part that is too big for the intended diameter of the hose either.

The bigger wonder is why the Hell they do it this way. Every fitting that uses heater hose could be the same size, but they aren't. Every fitting that uses vacuum could have the same size fitting on the manifold and on the part, but they don't. And it sure is not an issue to get you back to the dealer to buy parts, because it is well demonstrated that anybody who makes parts can make them this way too.

Edit: As soon as I posted that I adjusted my search strategy and found these things exist in multiple sizes:
https://www.autozone.com/fittings-an...tor/102831_0_0

My latest problem for next springs projects is solved, and now the clamp requirement has doubled.

 

Science.
Hot liquid that has expanded goes in (big tube). Heat is removed (heater core / radiator) temperature drops, pressure drops. This would create a vacuum / cavitation. In order to keep the pressure up, the exit hose needs to be slightly smaller. This probably isn't the best explanation, or using the right words, but I think you get the idea as to why hoses are different sizes.

 

https://www.hotrod.com/articles/why-...er-than-upper/

 

My question was not why one hose is a different size than a different hose. The question is why one hose end is a different size than the other end, of the same hose. The most flow you are going to get from that line is governed by the smallest restriction in it.

The hoses from the thermostat to the heater valve are big at the thermostat housing end, and smaller at the heater valve end. Then the hoses leaving the heater valve are small, but the ID gets big again at the heater core line. If this were some sort of velocity issue then the valve needs high velocity coolant going in to work but the heater core needs lower velocity? Not adding up that the vacuum operated valve needs a wee slight pressure tweak by necking a line down 1/32" or so.