Long AST to Reservoir Hose?
 

Apologies if this is covered elsewhere; I did not find what I was looking for with the search...

So I am replacing my radiator (and ast) and am also replacing all the hoses I can get to easily at the same time.

I had ordered all the hoses via part numbers posted in another thread, but my old ast -> reservoir hose must be a different part, as it is significantly longer. . Or is it a mashup of two oem hoses?

Pic below of the new (smaller) hose and the old one that I would like to replace. .

Should I just buy another ast -> reservoir hose and hack it together with the other to get the length? If there is a different p/n for the longer hose, I would greatly appreciate some knowledge!

Thank you!!! (And not just for potentially responding to my query, but just in general for everything on this forum!)

https://cimg3.ibsrv.net/gimg/www.rx7...c7052f4a92.jpg
AST to reservoir hose. Looking for part number of longer hose.

PS - anyone else thinking about stock radiator replacement, consider ordering new rubber mounts if you aren't sure if they have ever been replaced (pretty sure mine were original). My top mounts decided to split at the very last moment. Together.

Top mount: F285-13-363
Bottom mount: LFG1-15-202 (pretty confident those are the correct p/n's, but as always do your own research)

What part no. is your "short" hose?

Your "long" hose is actually at least 2 different parts.

My parts diagram shows that the part number for the AST to reservoir hose is N3A1-15-380C, which I think is the "short" hose in your picture. It consists of multiple pieces of hose, a joint (coupler) or 2, and protective sleeves, each of which also has its own individual part number.

The parts diagram shows that the reservoir tank ALSO comes with a section of wrapped or sleeved hose attached to it, with a coupler at the end.

These 2 hoses are coupled to give what would look like the "long" hose in your picture.

If you don't want to re-use old hose sections, keep the new "short" hose you already have and order the hose section that normally comes with the reservoir tank, including its coupler if you want to replace it too. Connect them to your "short" hose and you should be all set. The reservoir tank hose is 93-2407 (no.1) and N3A1-15-359 is the joint (coupler).

However, depending on what the part no. is for your "short" hose, you might need another section of hose, 93-2407 (no. 2) to get the full length of your old "long" hose.




https://cimg3.ibsrv.net/gimg/www.rx7...131c6b73f2.png

In section 1500 of the parts manual it shows the complete four part hose assembly as reference 15-277. This corresponds to part N3A1-15-380B. However, there is a note that after VIN number 200106 the part number becomes N3A1-15-380C. As discussed above the assembly is composed of four parts each of which has its own serial number.

If you look at the long hose in the picture you will see 2 white plastic hose joiners. Typically the overflow tank comes with that last little 6" section of hose.

I would just get that one piece from the old hose and hook it to the new hose.

You can also use 6mm vacuum hose for that overflow tank hose - since it's not pressurized you can use regular silicone. I've had my car using that for years with no problems.

Dale

This is exactly the issue. I know personally because one of the first things I did when I bought my FD was to change out all the hoses using a kit that Ray had at the time. I didn't think about that extra short section and just pulled the hose off the reservoir...threw the old hose away with all the others...then when I later got back to installing the new one, it was too short. I ran a section of silicone hose to extend the length for a few years until I replaced the reservoir with a new one for cosmetic reasons, and it came with the short hose already attached and I finally realized what had been wrong all that time.

Considering the risk of an overheated engine that whole set up around the AST seems a tad flimsy, particularly as it gets old. Would it not be better to replace the whole set up with something more robust. Four sections between the AST and the reservoir, come on man!

Or is designed to be the weakest link on purpose?

These four sections aren't pressurized, they go between the pressure-relief cap and the overflow tank. Rather than a separate AST and overflow tank, most modern cars use a pressurized tank that acts like a combination of both. I think it would be interesting to try something like that, but it would need to be mounted higher than the engine / water pump and there's not much free space up high in the engine bay.

We refill the coolant through the reservoir tank. So somehow the coolant flows back to the cooling system. Bit of a mystery to me. Something to do with atmospheric pressure and cooling fluid causing suction?

Again I am concerned about the general flimsiness.

Yes, the coolant expands when it gets hot and some of it gets vented through the AST pressure cap into the overflow tank. This will happen even if the four hoses aren't sealed perfectly. When the engine cools down hours after shutoff, the coolant contracts and the pressure cap allows coolant to be sucked back into the system from the overflow tank. If the four hoses aren't vacuum-tight, cooling system will suck air instead of pulling coolant back into the system. The factory low-coolant alarm should warn if this happens, but it's also a good idea to check the coolant level in the AST (or filler neck if your AST has been removed/bypassed). A single hose would be more reliable.

Need to be mindful to have the proper two way coolant cap.

Thank you
 

Sorry for my delayed response; 'had a member of my family in the hospital unexpectedly.. life finally getting back to normal now.

I just wanted to say thank you to all, the detailed and specific info supplied exemplifies why this forum is so fantastic!

Thanks all!!