Hi. I posted this on g35driver also but I hope you guys will chime in and give your ideas. Sorry if it's a long read but I think more details is better than not enough!

Here is what's happening: the car is a 2007 6 speed sedan that I've owned for 4 months. The car has been driving very well since I got it at 114 300km and now has 124 000km (78k miles). The only maintenance I had to do until now is one oil change that I did myself. I have an extended warranty that will expire in 2 months so I took it to the dealer for a good check-up, new spark plugs and fluids change (diff, transmission oil and coolant).

They called me back saying that they found some contaminant in the coolant. They also noticed that nearly all the rubber coolant hoses have expanded (swelled) and lost their rigidity. I went to have a look after work and there was nearly 1/4 inch of the pale green stuff floating on top of the coolant emptied from the overflow tank. I brought home this sample of what they had kept to show me:







At first it was floating and covering the surface but it adheres to surface so much that it ended up covering the walls of the bottle and nearly nothing floats on the top of the coolant (which looks clean/ allright). They said it COULD BE oil from a bad head gasket but they are not sure because none of the 5 mechanics there have ever seen something looking like this. We all think used oil mixed in there would have a darker brown color. They said it's not uncommon when a head gasket fails to find coolant in the oil but they have never seen the opposite. My oil has 5000km on it since I changed it and looks perfect and the level is perfect too. The oil it had before I changed it was just as perfect. Spark plugs were very normal. So they said MAYBE someone poured the wrong fluid in the coolant accidentally (NOT me for sure!)

I looked at the maintenance history from the previous owner and at 108 000km there was a CEL and he took it to his dealer where they changed the thermostat and purged the coolant (not a full flush and refill). They did not note anything else in the work papers.

I did my own investigation and searched the net for similar cases. I found 2 or 3 that had oil in coolant but no coolant in oil and all those that posted when they had it solved said it was head gasket failure. But on the pictures I can find on goole of oil in coolant the contaminant looks more brown than what I got. I also showed my sample to 2 other mechanics. One told me it doesn't look like oil, too pale : most probably someone poured some sort of leak sealer stuff in there or it could be just very old coolant that turned bad. The other is my trusted mechanic where I've been going for 10 years. He was working at at Honda dealer for 10 years before starting his own business and has always been very honest with me. He thinks it's oil from a head gasket or micro cracks in the heads or it could be from the oil cooler. He told me ''dealers are crooks, whatever happens, warranty or not, you'll be spending a lot of money there!''

And this the problem: everything I can make them change to confirm the diagnostic is not covered by the warranty. And being not 100% sure means that if my dealer pulls the motor and trans from under the car and open the heads and finds nothing broken it's not covered by the warranty and I pay 15hours at 120$/hour!

So for the moment I went with their suggestion: they replaced the worst hoses, changed the thermostat, radiator cap and flushed the system the best they could and filled with new coolant. Now it's wait and see. If a lot of crap shows again in the coolant we'll know for sure that it's oil and that it comes from somewhere inside the engine. I just hope that it doesn't take too much time if something has to show up because then I'll be out of warranty and this may be just what the dealer wants...to push back the problem!

I think I'll try to do some mixes in bottles with prestone and various oils in my garage this week-end so I'll try to do color and texture comparisons. And I'll do an oil change next week so it will be the moment to try to test the oil cooler in some way and put new o-rings to seal it at the same time.

Sorry for the endless text but this is quite a nightmare for me as this is a car I love and was hoping to keep for a long time!
Anybody ever had to deal with a major engine problem under warranty?
Any suggestions on what I can do to diagnose with CERTAINTY would be welcome !

Wait and see what happens. Check coolant after 1000 miles
Next step would be a compression test to confirm a leaking head gasket

Good luck

Telcoman

Unless someone spiked your oil it could only be coolant. If you think it may be something else I wonder if a local college would check it out for free?

A little update. I did some color and texture comparison tests of various liquids in bottles. I'm now 99.9% sure that it's oil. The closest result I got was new clean oil with a few drops of used oil mixed in. At least I'm sure that it was not ''stop leak'' type stuff or simply windshield waser fluid that was in there! After driving the car 600 miles some gunk came back in the system but not much. Hard to tell if it was just residues left after the flush or new crap. At that point it was time for an oil change so I did it and added fluorescent tracer dye in the oil (it's dark brown-orange when seen with the naked eye). About 150 miles later I checked what was in the overflow tank with a powerful blacklight. I could not really see any fluorescence, I thought maybe it's because not enough oil had the time to leak through. I'll check back in another 3-400 miles. Meanwhile I'm gonna do a hydrocarbon test on the coolant system tomorrow. I found a garage nearby that does it for cheap enough.

BUT the stuff that came out of the overflow tank after 750 miles, 150 of whitch was on new oil with the tracer dye, was a bit of a darker brownish-orange color. Here it is on the right:



Oh and my car does not have an oil cooler so that eliminates one possible leak area. I read somewhere in the FSM that it's normal for a RWD manual sedan not to have one.