My '00 S2k has been periodically overheating for the last few months.

The sequence of events is :

car starts up cold

after 3-4 min of driving, heat starts flowing from vents - feels OK

heat turns cold (not good!)

temp gauge goes up to 4 or 5 bars for a minute or two

heat is very cold (almost no heat)

heater suddenly gets warm again and the temp gauge drops back to 3 bars.

This is during typical granny-style driving around 3-4k rpm and 30-40 mph in cool temps of around 40-60 F.

Ther is plenty of evidence of overflow bottle being over-full. Coolant and coolant residue around the overflow bottle. I replaced the radiator cap, hoping for a cheap fix, but no dice.

Are there any gotchas in this system? For example, on my 93 RX-7, the cooling system can be extremely hard to purge of air, particularly if you modded it... newbies don't know this and often overheat when the ONLY problem is that they're a half gallon low on coolant (but it looks full). Does the S2K have strange quirks like this or should I just start checking other stuff like the thermostat?

There is no evidence of coolant leaking out other than through the bottle, and the coolant is clean (no oil). I'm hoping it's not a head gasket or other irritating problem like that.

Tonight when I parked, the bottle was basically full to the brim. I will check the level in the morning to see if it's pulling back correctly.

Thanks!
Brian

 

That makes me think : thermostat.

 

^ i agree.
try touch the hose on the driver's side (or the upper hose) while your car has those 5 bars. case of beer says that it will be cold or warm, not hot.

 

OK I will definitely look into replacing the thermo... I had it off once before about 18 months ago while doing some other work so I know where the bad boy is.

Update: Came out this morning, and the car had sucked about 1/3 of the 100% full overflow back. Opened the radiator cap, still low a quart. Put a quart in to fill the radiator up, drove to work... no problems.

 

air bubble? when you opened the system last, did you open the bleeder valve when filling up?

 

OK I went out to run and errand and I got more data.

Upper radiator hose was quite hot (couldn't really touch it for more than a second)... and very rigid. It was not soft like when it is cold. I don't have my IR heat reader thingy here, but I'd estimate the hose was over 175 F.

Overflow tank is absolutely full to the brim and there was coolant/water mix all over the innner fender area there.

To answer jzz30's question, I don't think I used the air bleeder when I did the valve job a while back... but it wasn't overheating for about a year after the valve job... now it is. To me, that indicates that that isn't my prob... however, I do agree that the valve is there for a reason, and perhaps I should look into it

Thanks for riding along with me as I investigate this

 

Id guess it is the thermostat too, same thing happened in my eclipse. Was about 10 degrees outside so over heating was not a problem but I only had about 120F in coolant temp so heat never worked etc.

 

I'm having pretty much the same issue and I just replaced my t-stat and fan switch (Mugen), so I know they're not the problem. Water temp never gets over 190 in my case -- even under spirited driving -- but the overflow reservoir keeps filling up to the brim and spitting coolant everywhere.

Any thoughts as to what might be causing this?

 

Last time I saw this on an s2k it was a head gasket, especially on cars with thicker head gaskets.

Original poster......this system is difficult to purge the air from. If you do a t-stat, fill it up per the manual, then use a turkey baster to pull air out of the rear bleeder (the one on the aluminum line on the firewalll with the rubber cap). pull it till you get coolant, then cap it quick.

It is also advised to run the car just till you hit 3 bars, then shut it off. While off, crack the bleeder in the front, you'll get some air there. You will always get more coolant in this way.

3 bars + hot heat means you're good. If the heat turns cold, even for a second, you have air.

Bigpurp....take the adaptor from a compression tester and air the cyls with shop air one at a time. Watch for the level in the rad to slowly rise. If it does, it's a head gasket. Copper spray sealer on the new gasket will cure it. PM VenomousS on this subject, we've been through it on his car.

 

Thx Billman. I'll run the test and see what happens (praying that it's not the HG).