A while ago I had my stock radiator swapped out for a Koyo as a preventative measure. Honda Type 2 Fluid was used. By a while ago I mean maybe 5 years ago...

I've been going over the car, checking things I should have checked a while ago, and noticed my coolant overflow reservoir was bone dry. The reservoir cap was cracked up pretty bad. I've already replaced the cap, washer, and elbow for the reservoir. The reservoir now has the correct level of Honda Type 2 Fluid in it.

On a completely cold engine (not run for days), in near freezing temperatures, I opened the coolant cap on the radiator. There was definite positive pressure, and maybe a few teaspoons of coolant spit out. I didn't even really take off the cap, just rotated it like I was going to, it hissed and spit like a shaken soda can, and I closed it reflexively.

I thought the system is supposed to be under slight vacuum if anything if the system is cold. I know the reservoir should always have liquid, and the tube should always be submerged.

My question now is - should I do a complete flush? Is the fact that the system was under pressure when cold cold concerning? The car never overheats, at least on the gauge cluster, and there's nothing to lead me to believe anything is wrong with the engine, or that there is a coolant leak.

Thanks for your responses. I'm going to be doing as much of my own maintenance as I can now.

 

Not an indication of a need to flush. But what is a concern is where the coolant went. Like is there a leak, old hose, etc. Or worse, a weeping head gasket (coolant being consumed in cylinder).

But maybe it was never fully purged of air when radiator swapped. That would be my bet. The air made its way out, reservoir coolant filled the void.

Do theair purge procedure. Park nose up (higher the better). Use a Lisle funnel. Open the front purge valve near front of valve cover until no air (be prepared for a bit of coolant to spill out).

Most important of all, make sure heat blows hot enough to burn fingers if held right up to vent. If not, you still got air.

You're extremely lucky. Because air in coolant is like ticking time bomb. Never know when its gonna go off. One day, driving casually down road, outta nowhere, engine overheats and melts down.

 

You may need a head gasket

I would do a leakdown test (engine cold) with the radiator cap off. See if any coolant pushes out of the radiator when you pressurize the cylinders.

There's only 1 way that residual pressure gets into a cooling system: engine compression

 

I opened the coolant cap again to see the level. No pressure, but I still haven't driven the car. The level in the radiator was 100% full. There was no burst of air, so just the little puff from when I first opened it. Like opening a can of soda.

I could be wrong, but if there was a leak anywhere, I think after 5+ years the radiator wouldn't still be 100% full.

The car blows hot air, hot enough to burn your hand.

Since I'm blowing hot air and the radiator is full - is it safe to drive the car with the topped off reservoir and see if the level changes?

 

Also, is it possible that the reservoir was empty due to the broken reservoir cap?

 

They have testers to see if combustion gases are getting in the coolant. Cheaper less equipment than a leakdown test.

 

I'm going to do a bleed per Billman's guide. I'll see how much air comes out/coolant goes in. Car never seems to overheat, per the temp gauge in the dash at least. Always 8 bars. I really hope my engine isn't borked.

 

Engine coolant replacement at this point in our car's life is every five (5) years or 60,000 miles. You're due for it based on time but I doubt you've driven 60,000 miles in the past 5 years so I'd not panic and just change it when we get rid of this snow and decent weather comes back -- say April or May .

-- Chuck

 

I agree Chuck that's a good time for me to do it. Do you have compression and leakdown tools by chance, and have you ever done them? After all of this discovery and going over my vehicle, I want to do those to make sure I'm alright.

 

I did compression and leakdown years ago after I set the valve lash but borrowed the compression gauges. (I have the gauges and tools for the valve lash.) I recall @Birdybog has the funnel and fittings to do the antifreeze swap, he's always been happy to assist me, and may have the compression gauges. He's off Otterdale Road on the west side so we're all pretty close. And there's at least an other couple of S2000s in the county as well as several down toward Yorktown.

Download the 2000-2008 Service Manual even if you have the paper copy since it's searchable something impossible with the paper copy. I just carry my old laptop down to the garage as needed.

-- Chuck