SR20DET coolant line simplification.

by ryandriftingfat on March 1, 2012

When you buy a JDM SR20DET swap conversion, there are some maintenance items you should take care of before dropping the motor into its new home. The OEM coolant lines are a mess, especially the lines under the intake manifold. You don’t want to try changing these lines when the motor is in, so this is my documentation along with some ideas to simplify the whole thing.

So this is what you’ll find from the factory. I’ve removed the intake manifold to get a more clear picture of what’s going on underneath.


What a mess. Let’s get to work.

From the factory, the S13 SR20DET has coolant feed and return lines for the heater core routed to the hot side of the motor.  The coolant line splits off behind the cylinder head to feed the turbo and there are also several wiring harnesses routed along the firewall.

When we swap these motors into LHD cars, most people loop the coolant lines back from the hot side of the motor back over to the cold side, adding additional hoses to all the other crap running behind the cylinder head. This makes working back there a serious bitch and looks nasty.

So here is a diagram of the OEM coolant line layout. Click to zoom.


This is what you’ve got right now, as far as hard lines go. I omitted one hardline at the back of the motor because it’s just one section of a two-piece tube and can be removed with bolts no problem.

So, going through the list:

  1. Coolant feed for turbo
  2. Coolant feed / return for heater core (solid tube all the way to point #8)
  3. Coolant feed / return for heater core (two-piece tube with a rubber coupler; rear piece removed in diagram)
  4. IACV feed / return
  5. IACV feed / return
  6. TB feed / return
  7. Water outlet for thermostat housing
  8. Coolant feed /return for heater core
  9. Coolant feed /return for heater core
  10. Coolant feed /return for thermostat
  11. TB feed/ return
  12. Hose connection to radiator

OK, so first things first. Let’s get rid of that big tube running from point #2 – #8. In order to do that, you need to consider a couple things;

  • How are you going to feed coolant to the turbo?
  • Are you going to keep the coolant feed to the IACV?

Do you need to keep the IACV? I can’t answer that for you, you’ll have to do some of your own research and that’s out of the scope of this article.

OK, replacing the turbo feed is easy. The S14 SR20 water neck has a fitting on it for the turbo feed. This water neck will bolt onto an S13 SR20 cylinder head no problem, making that turbo feed (point #1) unnecessary. You can re-use the coolant return and oil feed lines, but your coolant feed line will not work. It has a beaded slip-fit hose fitting and the S14 water neck uses a threaded fitting. You could try an S14 SR20 coolant feed line but in reality you should just purchase some stainless steel turbo lines for an S14 or S15. The stainless lines are easier to work with and have all the correct fittings you’ll need. Don’t worry if you have an S13 turbo, the lines will work with S13 T25 or S14/S15 T28. Alternatively, that means you can upgrade to an S14/S15 turbo without replacing your stainless lines.

S13 & S14 SR20 water neck comparison:


Now, IACV. This is more up to interpretation and application. Depending on the climate and the type of driving you do, keeping the IACV may be in your best interest. I do not daily drive my car and I live in California which is 50-70 degrees year round, so IACV is out.

If you want to keep IACV, then you’ll want to cut the tube running from point #2 – #8. Referencing the diagram above, you’d want to cut that tube down to about even with the tube running from points #3 – #9. That will retain the IACV feed lines at points #4 & #5. If you are keeping your heater, find some custom hoses that’ll point towards the heater core (now located on the cold-side). If you are ditching your heater, just get a short ‘U’ hose to loop the two coolant tubes.

One thing I want to mention – if you end up cutting down that tube, you’re going to be cutting out the bead-rolled end. Hose clamps will no longer have a solid surface to seat against and may pop loose. An alternative to that is to cut the bead-rolled end off the tube, cut out the section of tubing you do not need, then weld the bead rolled end back onto the end of the tube, to shorten the whole thing.

If you are ditching IACV, then the entire tube from points #2 – #8 can be removed. You’re now going to replace this section with a ‘J’ shaped hose. This means that the hoses & tubes at points #1 & #4 are gone and point #2 has been moved to the cold side or deleted. Now, you still need to get rid of point #5. You could cap it off; I’d recommend cutting the tube. If you decide to cut the tube, you’re going to again lose the bead-rolled end (meaning a hose clamp has nothing to seat against and could slip off). I couldn’t find a shop that had a small enough bead-roller to fit inside that tube, so we decided to cut the end off, then cut off the section we didn’t need, then weld the bead-rolled end back on. UPDATE: picture located at bottom of this post.

If you’ve gotten this far, you no longer have any hard lines around the back of the cylinder head and you’re feeding coolant to the turbo from the water neck. Points #1, #2, #4 & #5 are gone. OK, now the rest.

At this point you’re either going to have the the #2 – #8 hose shortened, or have looped the two coolant tubes connecting points #8 with #3. Whether your IACV is hooked up doesn’t matter the rest of the way. Now you’ll need to go to an auto parts store to find a hose that’ll work to connect point #7 hose to #10. The hose you need will be kinda shaped like a question mark.

Point #12 goes to your radiator, which leaves points #6 & #11 to deal with. They are coolant lines for the throttle body. Whether you keep them or not is up to you and you’ll have to do your own research there as well. Hook them up if you want, or cap / weld them shut if you’re not.

And with that, you’ll no longer have any hoses running around the back of the head. That’s how mine is and the only things back there now is my coilpack harness. I had so much room I could tuck the clutch line and brake booster line under the firewall lip, and I can still reach the transmission bolts from the top with no problem. To me that makes this work super worth it.

This is what I have now.


My IACV & TB coolant lines are cut out and hose from points #3 – #9 is shortened. The tube from points #2 – #8 has been replaced with a J-pipe and I added a flex section just to add some rigidity and strength.

EDIT 3/15/12;
Here is a better picture of how my coolant line has been modified. Any shop offering welding services should be able to do it for you.


Hope that helps, hit me if you have questions.

(Huge thanks to Alex on Ziptied for helping me with this).