Hey all,
I've got a stock 2007 with ~175k miles and after HPDE sessions my overflow tank is overflowing and burping out coolant. This last session was in 90 degree weather down in Angleton TX and we were running 30-35 min sessions.
There is a minor amount of overflow during the session, but as soon as I park the car I turn it off and pop the hood and slowly watch as the overflow tank level rises and rises until it starts spraying out. I don’t lose much coolant at all, and there’s never a puddle on the ground or anything. Just a bit of spray during the session on occasion and maybe a Tbsp of overflow once I’m off track. I did replace the overflow tank with a stock unit recently as the original developed a crack, and I visually inspected this one to make sure there aren't any cracks in it.

I've read a few threads in the racing forum and the majority of folks say that OEM radiator should be more than enough for stock cars on HPDE days, so I'm wondering if I have an airflow problem or some other issue? I don't seem to have the cracking on the stock radiator as there isn't any leaking near the filler neck, only at the overflow tank.

I'm 100% open to upgrading the radiator if needed, though I don't plan to do a Mr Sideways radiator even though I know it's great, because it's $1k with fans.

Any thoughts on what to check / do differently for track days?

Thanks!

 

Sniff test on coolant,HG may have failed

 

Coolant smells good. No oil/gas smell…
Also changed the oil and didn’t see any issues there.

This has been an ongoing issue for the last 3 HPDE weekends and I haven’t noticed any issues with the vehicle other than the coolant overflowing a bit.

 

I'd probably check the easy stuff like radiator cap first.

Also do you have a datalogger to measure your temps? I'm starting to get concerned about my temperatures as well:


ECT = Engine Coolant Temperature. Blue is the outlap, red is middle of session, black is the in/cooldown lap.

 

+1 for checking your radiator cap

Are your radiator fans working?

Is your radiator possible blocked?
https://www.s2ki.com/forums/s2000-ra.../#post24479465

 

Immediate shut down of a very hot engine with no coolant circulating can boil in isolated areas. Turn the heater and fans on High and idle for a few minutes and see what happens.

-- Chuck

 

Thanks for the feedback all!

@bad_driver Radiator cap looks good but obviously it's pretty tough to tell if it's failing. I've gone ahead and ordered a replacement OEM radiator cap just in case.
Unfortunately I don't have a datalogger at the moment so I don't know what my actual coolant temps are I've been interested in getting some sort of oil temp sensor and a data logger so that I can check both coolant and oil temp / pressure just to be sure things aren't getting out of hand in those 2 critical areas.

@azn akira The fans are definitely working as I see / hear them kicking in on normal driving. I haven't pulled the radiator yet to check, but wouldn't be surprised if it had some gunk on it. It's the original radiator and has never been removed, so after 175k+ miles it's probably accrued some crud lol.

@Chuck S I was thinking something similar, so the last few sessions I kept the car running for a few minutes after I came in, but didn't turn the heater on. I only let it run for about 3 min with the hood open though as I checked tire pressures and took off safety gear. Once I shut off the vehicle with the hood still open it eventually overflowed (probably took about 5-10 minutes).

I'm definitely going to get a new Koyo radiator, as a preventative measure to the OE plastic end caps breaking, but figured I'd check to see if there are any other areas that I might want to be aware of (or to improve on), even with a new radiator. I haven't seen much in the forums in terms of directing airflow or sealing off the radiator area like I have for other vehicles, so it sounds like Honda has done a good job of ensuring the majority of airflow goes through the radiator.

 

The overflow tank is an expansion tank. Sounds like your system is overfilled. What is the fluid level in the tank when the car is cold? It should be low enough so the tank can fill as the fluid gets hot. If the expansion tank is full to overflowing when you get off the track, it is probably working as intended. Have you ever flushed the system?

 

@blueosprey90 The coolant system has been flushed multiple times at the dealership and the level in the expansion tank is right at the minimum when the vehicle is cold. I don’t think the system is overfilled but it’s definitely a good check. After the first day of HPDE sessions and multiple small overflows, the next morning the fluid level was below minimum and I had to add fluid to bring the level back up.

 

It makes me nervous that you've had the system flushed several times "by the dealer". Not that I have anything against dealers, just that I would prefer not to trust my cars to them.

In any event, I'm thinking that you have an incipient head gasket leak (failure) or that you still have some air in the cooling system that you need to burp out.

Billman's coolant bleed - S2KI Honda S2000 Forums

I don't have any real experience with these issues on an S2000, but check the underside of the oil fill cap for a mayonnaise like substance of oil mixed with water. Also check the oil dip stick for any evidence of moisture in the oil. A compression test might be a good idea; and also there is chemical test that can be done to determine if there is CO2 in the coolant. A pressure test on the coolant system can also be done.

But having said all of that, on my MGA, I had a cracked cylinder head that I was never able to diagnose via the usual methods until there was just too much of the mayonnaise under the oil fill cap to ignore. I pulled the head and had it crack tested and I had a tiny crack in one of the combustion chambers. My car, however, had "passed" the compression test and the coolant system pressure test; and the car never gave off a white smoke indicative of coolant getting into the combustion chambers. And for a while I lied to myself about the traces of mayonnaise under the oil fill cap until lying to myself was no longer an option.

But the car should not be bubbling over after a run on track. A group of us have had maybe an average of six S2000s at Watkins Glen over a period of about 10 years and in 95+ degree temperatures at times, and no one experienced such symptoms.

Good luck!