I have a 2003 350z with only 48k miles running an old school top mount kit with the usual supporting mods: fuel, tune, Plenum spacer, etc...mild 7 psi

The car spent most of its time in CA and I now drive it in AZ. The car doesn't like the heat, especially at highway speeds. I have the water temp alarm for Defi sensors set at 212 F and I can easily hit that just cruising at 85 on highway.

I've done a lot of research and have changed a lot of things to bring temps down w only minor improvements: cheap/thin dual core alum radiator (all I could fit), aluminum shroud w/spaal fans, 70/30 water/coolant ratio w water wetter, removing cowling....New lower temp thermostat.

The above changes have only resulted in moderate improvements....

Sealing front of hood (missing gasket so I taped it to test)
Better hood venting (have side vents but nothing over top of engine)

Better undertray and fender liner seals (missing the fender liners so maybe too much turbulence behind radiator?)

I've read a lot of posts here and am trying to solve this but it feels like im missing a big factor. This started w oem fans and radiator....maybe I should go back to that since my problem is elsewhere. I think that overheating at highway speed is a big hint at this being an aero problem. Are fender liners that important? Could it be a water pump issue?

Please help this electrical engineer out before i part this thing out and start over.

 

Do you have dams installed between the bumper and core support? If not, that will cause a huge airflow loss around the sides, especially if you don't have the fender liners in place. There should be some plastic air guides/dams on either side of the radiator directly behind the bumper. You can also add an air dam at the top of the bumper around the hood latch. For the bottom, I recommend an aluminum undertray. Since you're FI, hood vents, above the engine are almost a hard requirement. But before replacing your hood, make sure you have proper air guides/dams in place around the bumper/grill.

With only 48k miles on your Z, I sincerely doubt a water pump failure. I've never heard of a 350Z water pump completely failing either (not even shaft seals). They are driven off the timing chain and the primary mode of failure is not impeller damage or shaft seal failure, but rather the outer O-ring seals. When those outer seals fail, they usually do so in sequence, allowing coolant to drip out a wheep hole behind the AC compressor, giving you time to notice and repair before you have chocolate milkshake in the crankcase.

I'm a huge fan of the Koyorad 48mm (P/N: HH021568). That rad works fantastic and it's a *mostly* drop in fit. I'm not FI, but I'm running with it because I don't trust plastic endcaps. I prefer the factory radiator fans over aftermarket, no comment on Spaal, never used their products before.

Also, make sure you thoroughly bled the air out of the system. I cannot stress that enough. So many people don't follow the FSM procedure and open the air bleeder valve near the battery box when filling with coolant. This traps a huge amount of air in the system and can lead to hot spots forming! The obvious sign of this issue is when your heater doesn't blow hot when idling (air trapped in heater core).

Good Luck!
-Icer

 

Thanks for taking the time to respond. I have the air guide over the top but not the sides. I did install an alum under tray already this past weekend. I will locate the side pieces...can't believe I didn't know those existed but found them on diagrams this morning. The fans I am running are crazy good...best electric fans I've ever owned. I like sticking with factory on those too but went Mishimoto junk route and then ended up upgrading to these. I'm running a very cheap radiator because of its slim construction. I'll measure to see if that Koyo one will slide in there.

 

You need all the factory aero, it wasn't put there for fun, I don't know what your bay looks like but the Koyo cross flow and OEM fans should be more than enough. I have all of the above and even with the heat from my headers I don't see anything above 190 while cruising.

 

I run the koyo in the gulf south heat, and while it is not quite pheonix heat, I still can run cold AC and maintain 190s water temps in 105 out door temps on the highway. Fender liners, undershrouds and the side deflectors are basically required. any fan system is likely worse than the oem setup. SPALs are great, but when paired with the mishi shroud are probably worse than the oem setup, especially if they are only on low speed trigger.

I also have had to pull my condensor and clean it out at 200k miles because it was partially blocked just from road crud over the years.

 

Yeah, I suspect that the shroud is not helping. Honestly, as an engineer, I can see advantages to the geometry of the stock shroud. A flat piece of aluminum would be a much simpler design that Nissan would have opted for if it was truly effective. I haven't touched a Z33 front end in more than a decade and I bought this on in April just to save it from being parted out. I'm going to the junkyard this weekend just to refamiliarize myself with the stuff around the bumper support. Fingers crossed that with all of the plastics back in, the alum undertray and the fender liners all being back in, I can get back to normal temps. The only other item I don't like in this set-up is the coolant lines running to the turbo. I have the turbo hot side wrapped very well and it's under a blanket but coolant ultimately needs to run in that super hot environment. I'm wondering how much heat is being transferred into the coolant during that flow.

 

For sure....I'm just unfamiliar with what should be there since I bought this car from a guy that had it stuffed in a garage for a long time. I'm piecing it together little by little. I'm going to be pissed if I changed radiators, fans, shrouds, t-stat, thermal wrap, etc. and all I needed from beginning was better ducting.

 

The radiator is definitely a NEED, but the Mishimoto shroud is notorious for overheating on track, so it's not helping you at all. Thermal wrap should be mandatory on FI cars, my car isn't FI yet and the header heat is enough to flake off the "foil" off the heat sleeves protecting my AC lines. I'm going to switch those to the Lava rock stuff as that can handle more than the typical silver stuff.

Ducting is king, a lot of people underestimate its importance. If you need any info, or pictures of the front end don't hesitate to ask!

 

Here's a diagram of the core support. Parts #7 and 12 are what you need for proper aero. Sometimes these get chopped when routing plumbing for front mount intercoolers. Perhaps that's what happened in your case?
Cheers!
-Icer

 

Thanks....already sourced those and getting them this weekend....I'm probably also fabricating a carbon fiber duct of some sort because I'm knee deep in this now and also why not...lol. Thanks for all the help.

 

Don't underestimate the benefits of proper vented hood either. I run a mishimoto radiator with OEM fans, fender liners, aluminum undertray, and an MCR hood. Momentum top mount with a G35-900. I'll only go over 200 sitting idle on a hot day, but the fans kick on and bring it down pretty easily.

If you're not already, consider running E85 as well. Has good cooling benefits when paired with everything else.

 

Nice ride. My hood is vented but not in the middle. My biggest data point is that my temps only rise at highway speeds. I think I need to get rid of turbulent air behind the rad and I need venting in center of hood.

 

 

Car looks awesome, I love the Volk GTS (used to run those as well back in the day). Mine is also an '03, so small world here!

It is a bit odd that's overheating at highway speeds...does seem like there's some kind of issue with turbulence and getting the heat out...also curious if you're even able to get the oem aero pieces behind that bumper...my chargespeed bumper has that issue with the intercooler (not enough room really). The heat in AZ is serious...I do think there's a good chance a different hood would help, but might have to look into the radiator and fan/shroud combo as well.