Hi All

I attended my first autocross event this past weekend and had an absolute blast in my ‘07 350Z! But was disheartened when I got back to the grid after my final run, popped the hood, and smelled some coolant. Then I actually saw it isolated on the drivers side of the under-tray and there was not much (maybe 1/4 cup?). My running theory is that the more aggressive driving caused some “sloshing” in the overflow tank - and some coolant found it’s way through the drain port on the top of the overflow bottle.

So question for the group - is this common for 350Zs when autocrossing? Nobody else there seemed to really think it should be doing that but the pattern of the spilled coolant aligns EXACTLY with the drain tube.

For future events, I’m wondering if I should just leave the coolant level more between the Min and Max when at cold temp vs right at Max as Nissan recommends.

Thoughts?

Some additional notes/observations:
- Coolant was filled to Max line in the overflow bottle at cold temp per Nissan specs.
- Car temp never got hotter than a typical Sunday cruise; never close to overheating.
- Coolant level at high temp was not filling the overflow bottle (as it shouldn’t be), so it didn’t get “pushed” through the drain on top.
- After replacing many cooling system items over the past couple years, this is the first semblance of a “leak” after dozens of drives.

 

Is there any white smoke from the exhaust?
Any white film under the oil fill cap?
What is your coolant : water ratio?


Check hoses around the engine bay as you may have a small leak when coolant pressure is at it’s highest … check around the throttle body, the OEM oil cooler, and heater-core hoses. If youre smelling coolant it’s likely hitting the exhaust manifold and burning up.

I would look into a compression test and a leak down test -

I can’t imagine enough coolant sloshed out of the tank via the overflow port.

You’ve provided good information

 

Could be just coming from the radiator cap. If you have upgraded your radiator, it may have higher capacity than the OEM so the overflow tank level is not quite right.

 

Thanks for the quick responses. And sorry my posts are sorta wordy, but just trying to get all the info out there for help but also for potential future searchers (you're welcome autocrossers of the future with this very specific issue!)

- No white smoke from exhaust or any film on the underside of the oil cap, I really don't think this is head gasket related. There was visible coolant on the under-tray and I can track the white residue after it has dried. It's not anywhere near the head/block. Coolant is 100% isolated to the front driver corner. Also, the 1/4 cup mentioned in the original post might have been overstated - it could very well be just a tablespoon or two...hot/thin liquid tends to spread I suppose.
- Coolant ratio is whatever the premix Blue is from Nissan, I think 50/50?
- All hoses have been checked (HR doesn't have an oil cooler I believe?) There is no coolant residue - or was there any liquid coolant day of - anywhere higher than the exit of the overflow drain hose (rules out TB lines, hard lines, line TO the overflow, crack in the overflow, thermostat, filler neck, crossover pipe, etc.). Only hose with a sign of coolant residue is a couple drops on the top of the lower radiator hose (brand new as of last year) and that hose definitely does not appear to be "ground zero" of the fluid pattern based on the residue on the under-tray. Oh and the radiator cap is brand new as of end of last Summer.
- Another note about the smell, I was able to detect a faint smell coolant when my OEM radiator had a hairline crack in the end tank causing it to seep so I don't think it needs to be burning for there to be a smell.
- Last note, at the event I did my best to not burn the hell out of my hand - but was able to fish the drain tube up to inspect the exit and it was not dry. It wasn't actively dripping, but it was wet. And I guess now that I look at the pic below, there is some coolant reside on the end of the drain hose...

I haven't had a chance to get under there for a better view, but here's my best attempt at a picture using a mirror. This is taken from above the engine bay, with a mirror down by the under-tray reflecting back up to the potential culprit hose. Another big clue is that the damper block (that I guess is just on roadsters?) is that mass on the right had side of the picture where you see some white/blue residue - and the drain hose run ends about halfway down that block. And guess where there is and is not coolant?! That's right - at the exact height of the drain hose. Also residue on the underside of said block - which is about equal height as the lower radiator hose...so it seems almost impossible for a leaking lower rad hose to get coolant up there.

 

you misunderstood. The radiator cap might spew coolant because it is in fact working correctly. The symptoms you describe sound to me like pressure related release. second possibility is are your hoses still using the factory pinch clamps? those become weak over the years. I replaced all of mine with worm clamps when I replaced all of the hoses. try running the coolant level at the min instead of the max line and go do some hard driving during the hottest time of the day.

 

Spew coolant from the cap itself, or spew it into the overflow tank as designed? I think I'm picking up what you're putting down. Higher capacity rad (which I believe the Koyorad 36MM is?) + rad cap working correctly = higher amounts of coolant into the overflow tank. So when I refilled my coolant after the rad swap and leveled it at MAX when cold, that could be too high - despite what Nissan calls for - because there is more coolant in the entire system than Nissan accounted for with their MIN and MAX measurements. Am I understanding that correctly?

The only thing I'm still stumped on is the "pressure related" comment. There's no way for the overflow to pressurize because it vents to atmosphere. Are you just saying the pressure from the cooling system itself is pushing higher amounts of coolant into the overflow - basically the same thing I laid out above? If all of my assumptions above are right - then moral of the story is there is nothing "wrong" and that everything is working as intended - just with too much coolant. And this is the first time I'm noticing it because no driving on the street will mirror the hard cornering when autocrossing. So it could be "sloshing" but it is only finding its way out of the overflow because it's likely overfilled.

I will say, when at operating temp, the coolant level in the overflow fills probably 3/4 of the bottle which tells me that with hard cornering, the coolant could absolutely congregate to one side or the other and hit the overflow level.

Regarding the spring clamps, I replaced all 4 spring clamps with OEM Nissan ones when replacing the radiator and hoses last Summer. Only clamp I didn't replace was the water neck to overflow clamp.

Thanks for all the speedy replies, guys!

 

Sounds like the tank is getting full from the expansion of the coolant and its sloshing around out the vent. I wouldnt worry much about that at all. Maybe just lower the level a bit. Glad you made it to your first event though, Im sure it was a blast. Were you able to start pushing the car at all? What tires and pads?

 

Fwiw, my upgraded radiator came with a cap that would leak under track conditions, replaced with a z1 cap and haven't had any issues since.

 

Thanks guys, I’m going to get underneath and take a closer look and clean it up a bit when I get a chance. I’m sorta shocked I seem to be the only one experiencing this though. What level do you all keep your overflow tanks at on track/autoX days?

On the topic of the aftermarket radiator and cap, the HR’s cap is not on the radiator itself, it’s on a filler neck. So that’s sorta null and void for me.

If anyone else reads this, and has experienced the same phenomenon - chime in. I don’t know how these overflows don’t spill out more often quite honestly. The side with the drain narrows a bunch, so a hard right turn sends a ton of coolant from “the deep end” into the equivalent of a kiddie pool.

EDIT: I got curious, and looked up a DE overflow. That makes much more sense with how deep it is! If you’re curious too, take a look and compare an HR vs a DE overflow tank. Makes total sense why this wouldn’t be a blanketed 350Z issue.

 

I run a sealed can on mine, keep just enough in it to not let air in, It usually barely expands. I run Evans coolant in my Z, it doesnt expand much at all. Could be a good option to try. Its expensive but awesome stuff.

 

Completely sealed, or is there a tiny air vent? Wouldn't the expansion in a sealed can be a ticking timebomb? I'm sure you know more than I do, so mostly asking just for educational purposes.

I just ordered a generic small aluminum expansion tank cylinder that I'm going to mount over where my stock airbox was (have Z1 CAI right now) and run my main expansion tank drain line into that. So any drainage will just trickle into that vs. spill out. This way I can run an adequate amount of coolant without worrying about spillage on the few Autocross events I'll be doing a year. It has a small vent hole on top, so not worried about pressurization and if my cooling system does for some reason fail, it will still have a 'way out'. Plus it'll be easily removable if I decide I only want to run the setup on AutoX days.

One last comment on the design - because the more I look at it, the more I wonder what Nissan was thinking. When I was looking at the different years of Z expansion tanks, I think Nissan learned from the HR and revised it on the VHR so the vent tube is in the top middle and not at the shallow end of the tank. Just look at the HR one - the drain tube originates behind the cap in this picture - look how much coolant resides in the "deep end" and at the cold "Full" mark, it's probably around a level where those black numbers/letters are on the right. A few hard, prolonged right turns and coolant will most definitely find it's way out of the drain...it's almost like it funnels it directly towards the vent.




For context, here is how Nissan adjusted it for the early year VHRs. Notice how the vent is in the center - making it more difficult for fluid to reach in during 'sloshing'?

 

You're right - it was a total blast. Already ordered and received a helmet for myself for upcoming events. They're long days, so it will be hard for me to find time to make more than a handful a year, but I definitely want to keep at it. I pushed the car closer to the limit than I ever had before, and it was a blast to be able to do so in a controlled environment. Tires, I run Firestone Indy Firehawk 500 and just OEM pads. I didn't change anything up for this first outing and likely wont for future outings until I am sure I can make it a more regular thing. I just had an amazing time being able to drive the car to the best of my ability - learning that I have a lot of learning to do

 

thats cool, its definitely fun and humbling to get on track. I would recommend some good pads and fluid, the hawk hp+ are a good track/street pad. It will be much more fun and safer. one of the worst feelings on track is a soft pedal when you cant stop. saw your question on the tank, yes its completely sealed, its just a generic mishimoto aluminum tank. As the coolant expands it fills the tank, then lowers once it cools. Its not much at all, just keep the can 1/3 full. As I said I run the evans coolant that doesnt really expand much at all so that prob. has alot to do with it

 

Don't know enough about your particular setup to judge anything, but just in general the DE cap is designed to open at 1.3 bar. If the system was completely sealed and full of fluid you could run a risk of overpressurizing and blowing gaskets, etc. But I'm guessing the air in your can is enough to keep the overall pressure safe.

As far as pads, good pads go a long way, but also proper braking technique can make your pads and fluid last much longer. Hard brake initially, threshold brake, then start to release as you get to the turn in point. Never drag the brakes into corners .

 

yup good point Dr!

 

Just wanted to let OP know that I used to have this problem all the time when autocrossing my 07. I flipped that line and it now runs up along the top of my coolant tank and drops off the passenger side and it no longer sloshes out.

 

Humbling for sure - it was a "Novice School" which was extremely helpful to learn from those more experienced that I. Part of it was being able to ride with the more experienced drives, and two of my rides were in Lotus Elise - the combo of the driver + car made me feel like my runs were driving in a Sunday afternoon parade!

Technique is the name of the game right now - I am the weakest link by far. But when the time comes for new pads, I'll definitely be upgrading.

This is a relief to hear that someone else was experiencing this. I just couldn't imagine HRs doing any hard cornering without this happening. That being said, my solution a catch can for the spill out. It's set to arrive today and I'll get to it when I get to it - priority is to build a flower bed for the Mrs this weekend. But when I get it set up, I'll be sure to follow up with you all.