Recently, my NA’s passenger side Throttle Body (TB) coolant line sprang a leak. Here’s an underside picture of the upper plenum showing the location of the leaky hose
 (Note: Picture is of a TT upper plenum – not my Z’s).
After studying this problem a bit, I decided I’d rather keep the coolant lines operational. I know some have modified their Z’s to eliminate this problem – from a safety standpoint I wasn’t comfortable going that way! Instead, it looked pretty easy to install a new hose AROUND the problem! The yellow dashed line in the picture below shows how the new hose was run.
I DON’T KNOW IF THIS PROJECT CAN BE DONE (as easily) ON A TURBO ENGINE – THAT ENGINE HAS ADDITIONAL PARTS WHICH COULD MAKE THIS HARDER TO DO? Coolant connections differ as well!
TOOLS AND SUPPLIES This project only requires a few tools and supplies, here’s what you’ll need: - Three feet of 5/16 hosing, mine was labeled 50 PSI for fuel/emission applications. - One foot of 5/8 coolant hose. This is used as an outer jack for insulating and protecting the new line. - A 12-inch length of thin solid wire, some tie back cord or a short bungee cord. - Single edged (new) razor blade. Wrap 3-4 turns of duct tape lengthwise around the dull edge of the blade. This really helps in holding the blade when the time comes to cut one of the under plenum hoses. - Various other items: ratchet and sockets, razor cutter, and long needled nosed pliers -- Very nice for reaching hose spring clamps in rear of engine bay – I consider them indispensable for Z engine work!
STEP BY STEP INSTRUCTIONS
I wrote these instructions for part-time mechanics of all skill levels – you'll need to decide if you can perform this job safely, without causing harm to either yourself or your Z! 1. Remove all of the items located on the passenger side of the engine bay. Doing this probably takes as much time as removing the old leaky hose and installing the new one. - Battery
- Cruise control assembly – use a cord or bungee to pull it out of the way
- Golden bracket held by 4 bolts to side of plenum and vacuum line.
- Wiring harness and bracket
- Intake plastic hardpipe and hose fittings 
Tip: Removing aged vacuum lines from fittings is easier if you gently pry up on the hose ends with a small flat screwdriver and spray on WD40. It lubricates into the fitting and helps loosen things up. I don’t like to use silicon spray for vacuum lines – not sure if it will impact the O2 sensors? 2. Remove old hose spring clamp holding hose to the rear coolant fitting. It helps to spray the hose end with a little WD40 and then to slide the clamp onto the metal plumbing. Slit the hose end with an Exacto knife and pull the hose end free – a small amount of coolant will leak out. 
Cut the OLD hose end right above the rear PCV metal hard-line – this gives enough room to route/connect the new hose to the fitting.
3. Remove the old hose spring clamp on the fitting located under the throttle body. Slide clamp UP onto the metal plumbing and secure it up and out of the way with a small length of solid wire or cord.
 4. Slit the hose and pry it free from the metal fitting. Use a rag to catch any coolant – might not want it dripping down to the alternator? 5. The old front hose has to be removed to make room for the new one. Picture shows where it needs to be cut -- I thought this part was going to be hard to do?
A single edged razor blade was how I did the job -- hose is cut just at front side of the mid-plenum nipple fitting. Amazingly easy!!!
 TIP: Wrapping the thin blade with a few turns of duct tape made it easy to grab and hold with two fingers. The under plenum fitting kept the hose from moving around – all that was needed was to position the blade from below and give it a firm push! 6. Pull the old front TB coolant hose free. 7. Insert one end of the new hose (at mid-plenum) and push towards the underneath of the TB – a thin long bladed screwdriver, inserted under the TB throat, helps to guide it forward.
8. Warm hose end a bit – I used a cup of hot water. Lubricate inside hose end and nipple fitting with some engine oil and re-connect the hose to the fitting. Attaching it is easy to do when the hose is warmed-up and lubed! Untie the spring clamp and slip it down and over the new hose end (lubricating with a little WD40 helps too).
9. Cut a 4 inch length of the 5/8 inch hose, slip it onto the new hose - sliding it down under the TB area. Be sure to lubricate it too - makes the slide down nice and easy!
9a. The outer hose is used to position and hold the new coolant hose in-place. I not sure if this was really needed – but I figured it couldn’t hurt?
10. Route the other end of the new coolant hose down under the vacuum hard pipe and into the rear of the engine bay.
11. Slide the remainder of the 5/8-inch outer (protection) hose over the hose end and down towards the vacuum hard pipe at mid-plenum. DO NOT slide the outer protection hose under the metal vacuum line – things won’t fit back together right!
12. Verify that the outer protective hose doesn’t interfere with the coolant line connection. If the outer hose is too long – just trim it back a bit. Idea is to have it just resting on the PCV rear metal line. Carefully check and see where the new hose connects to the rear coolant line -- cut the hose to length.
13. Partially re-attach the mid-plenum golden bracket using top two bolts and verify everything is going to fit back together well. Idea is to make sure the 5/8-inch outer hose jacket doesn’t interfere with anything.
14. Slide new hose onto rear coolant line nipple and slide spring clamp back into place.
15. Tighten down the golden side bracket, re-attach the metal vacuum line assembly, re-install side plenum wire harness/bracket, TB intake hardpipe, re-install battery, cruise control assembly and throttle body hard pipe. Don’t forget to reattach any vacuum hoses that you may have removed too – there are a few in that area.
16. I used a wire tie-wrap to secure the new hose to the rear section of the upper plenum side wire harness assembly. Thought this would be a good way to reduce any hose "flexing" due to vibration? 17. Start engine and check for any leaks. Hope you NA owners find this helpful? It may be possible to do this same type of repair on the driver’s side too – it's something I'll consider if a leak occurs there. REMEMBER: No Plenum Pull Before Its Time!!! BONUS SECTION To TOTALLY eliminate both coolant pathways under the passenger side TB – look at this picture.
- Remove both rear spring clamps and hose ends from their coolant line fittings and cut off any excess.
- Use a short length of 5/16 hose to connect the two coolant fittings together as illustrated.
There have been debates about whether or not the TBs need to be warmed by these lines - a tt.net search will yield many posts on this topic. You'll need to decide for yourself whether or not eliminating them presents safety risks? DISCLAIMERS… READ AND FOLLOW ALL SAFETY PROCEDURES RECOMMENDED IN THE
NISSAN SERVICE MANUAL FOR WORK ON THE 300ZX Z32 ENGINE. . MAKE SURE CAR ENGINE IS COLD AND THE COOLANT SYSTEM IS NOT UNDER PRESSURE. HAVE SAFETY EQUIPMENT HANDY IN CASE OF AN ACCIDENT AND DISPOSE OF LEAKED ANTI-FREEZE PROPERLY. ANTI-FREEZE IS VERY TOXIC!!! -- KEEP CHILDREN AND PETS OUT OF THE AREA! YOU ARE RESPONSIBLE FOR YOUR OWN SAFETY WHEN WORKING
ON YOUR CAR. THIS WRITE-UP IS AN EXAMPLE OF ONE WAY TO PERFORM THIS MAINTENANCE, IT MAY CONTAIN ERRORS AND NOT BE THE SAFEST OR BEST WAY TO DO IT. YOU ARE RESPONSIBLE FOR DETERMINING HOW THESE REPAIRS SHOULD BE EXECUTED IN A SAFE AND CAUTIOUS MANNER -- AUTHOR IS NOT RESPONSIBLE FOR ANY HARM TO YOU, YOUR CAR, FUTURE GENERATIONS, YOUR PROPERTY OR TO OTHERS WHILE OR AFTER PEFORMING THIS OR ANY OTHER AUTOMOBILE SERVICING...
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