I just bought an AP1 S2000 last week. I searched for a while and found a clean, low mileage car. It's lightly modified (intake, exhaust, suspension) and everything checked out on the test drive. No CEL's, everything ran strong and felt good.

After getting it home I noticed it was consuming coolant from a 100 mile drive home - overflow tank went from max line down to min. Temp gage never passed 3 bars. No visual evidence of oil / coolant contamination. I checked all the normal spots I've read about here (hoses, intake manifold gasket, radiator, etc.) and never found any leaks. When the car is cold, a coolant pressure test doesn't reveal anything so I'm assuming the leak only happens when everything heats up.

Is this what I think it is - cracked block AND head? View is from underneath the car looking up at the block/head interface just below the exhaust manifold on cylinder 3.

 

If the coolant in the car is blue, the leak will show blue as well. There is no mistaking it. That doesn’t look like coolant.

 

The coolant is blue but i can't find it dripping. Is what I'm looking at just normal casting imperfections?

 

I have not heard of blocks on these cars cracking. It is normal for the overflow tank to go up and down.

 

Nervous new parent. Your baby is fine.

Normal casting marks, probable normal fluctuation in coolant level. Expands with heat, etc.

Does the heat blow burn your fingers hot right next to vent?

If not, bleed air from coolant. Easiest way is fet Lisle type funnel. Park nose up. Attach funnel to radiator cap, fill with correct coolant. Idle till fully warm, heat works, etc. Give a few revs. Keep funnel topped up.

Once no bubbles even with rev, good to go.

 

I probably should have mentioned the following in the original post: the engine bay smells like coolant when it's hot and there's a ~2 sq ft. stain of coolant under the rear passengers side of the engine block. I hooked up the coolant pressure tester hoping I'd see where the leak is actively coming from but I haven't seen a clear drip yet. So far I haven't been able to reproduce the leak on a cold engine. The only things I see in that area that could leak are the oil cooler lines, head gasket area, and heater core / hoses. I've read about people having leaking intake manifold gasket migrating too. Everything I've checked comes back dry, the only thing I've found that seems like a potential cause is those markings on the block. I assumed it was cracks and maybe the block needed to heat up and expand before it started leaking. I guess next step to confirm / rule this out is to start the car up and get under it to observe. I'll let you guys know what I find - but unfortunately it has to wait for another day since family duties call.

Thanks everyone so far for your help and advice. Here's to hoping I'm an idiot and it's something else I haven't caught yet.

 

Get the free oil test kit from Blackstone Labs, and when you change the oil and filter take a sample mid flow and sent it to them. Any contaminates like antifreeze in the sample will be noted. They have a data base of the S2000 engines and will note how your sample compares to it.

Complete fluid change is a good way to establish a zero baseline for maintenance. Plenty of information here on this. Note some maintenance, like antifreeze is on a time, not mileage basis.

-- Chuck

 

The easiest solution is to buy a coolant dye and pinpoint where the leak is coming from.