So I have a 2007 RX8 with 69xxx miles. In the past couple months, it has started to have issues. First, it began misfiring on startup. I took it to the dealer, and they confirmed that two coils were toast. They wanted to charge me 1200 to swap them, so I had it towed home and replaced them myself (also swapped in new plugs).

The car drove well again for about 6 weeks, and then just recently I noticed that after I had let it sit for 2 or 3 days without driving it, it would chug and misfire on startup (flashing CEL) and emit a plume of white smoke from the exhaust. This would pass after about 15-30 seconds and the car would drive great. This would not happen unless the car had been sitting.

After sitting overnight, the car starts right up and does not misfire but emits a small amount of white smoke from the exhaust for a couple of minutes.

So I checked the coolant level and it was down around the 'L' line - and I had just recently checked it. So coolant is going somewhere, and there isn't any on the ground under the car.

My working thesis: there is a small coolant seal leak that allows coolant to seep slowly into the motor, and thus the symptoms are worse the longer the car sits. Surely this seal failure will get worse and worse (quickly), and I know this means the motor needs a rebuild. Please chime in if you think my diagnosis is incorrect.

My question: Where is the dealership going to try to bend me over with respect to the warranty on the motor? The car is still under the 'core' motor warranty (went into service in 2008). I want to make sure I have all my ducks in a row before bringing it into the dealer just to maximize the chances that they attribute the issue to a 'warrantied' part failure.

The car had always been serviced by the dealer until I purchased it at 58k miles. Since then, I have performed service. I've done 3 oil changes (I can dig up the receipts for oil filters). Right now, the only issues with the car are a coolant sensor that occasionally comes on (I check the coolant level frequently, it's never been low) and a CEL for a bad rear o2 sensor (the one that's there for emissions purposes). And as I stated before, I changed the coils/plugs myself with OEM/NGK. The car has never overheated during the course of my ownership, and exhibited none of these issues until recently so I am assuming the previous owner did not overheat it either.

I figure I may have to get these things taken care of before taking the car in, but wanted to get the popular opinion on everything as this is the first time I've had a major issue with one of my cars that could potentially be covered by warranty. Thank you all in advance for your help!!!

 

Yup, sounds like a coolant seal failure to me. My guess is that you did actually overheat it at some point, but didn't notice. The gauge cluster needle doesn't start moving until 235F, but you can damage a coolant seal as low as 220F. 15F of danger before the needle even twitches, and most people don't even notice a twitch.

The biggest difficulty you will probably face is getting them to test for a coolant seal failure, instead of a typical compression test. Make sure you go in with that clear and up front.

I just took a look through the service manual for 2007s, and I don't see a procedure for the dealership in this case, so you may have to fight with them a bit on how to confirm it. A cooling system pressure check is probably the easiest for them, however it might be easy for them to pin that on any other part. The 2nd easiest method is to let the car sit for a day or so, crank the engine over very briefly to throw any possible coolant around (but not out of!) the engine. They will need to do that while the fuel cut is engaged (don't want the engine starting), then pull the plugs and inspect for coolant. If coolant is there, it's an easy diagnosis.

 

What about just asking them to leave it in their parking lot and start it after 2 days? What else could they attribute the huge plume of white smoke to?

 

And just to clarify on my question: what other 'contributing' components could they possibly try to pin this on that I should make sure are working correctly before going into the dealer?

I'm just trying to avoid a situation where they say 'coolant hose was cracked which contributed to overheating which contributed to seal failure, no warranty for you'. This is just an example by the way - hoses are fine.

 

If you want to be sure, get your cooling system pressure tested before going to the dealer, pretty cheap at most corner shops.

If the dealer is reasonable, they won't argue about any of it. But if the rep is a moron....

 

Thanks for the advice! Just for my own understanding - what will the pressure test show? Will it be able to conclusively prove a coolant seal fail? Is there a particular spec (PSI) that the test needs to be run at?

How much do these tests typically run?

Thanks!

 

Actually, scratch that, i was responding while busy with something else. A pressure test will fail, and that won't prove anything

Basically, there ISN'T another reason for excessive white smoke after a cold start. Even if you have a cooling system failure elsewhere in the car, it still won't directly cause any white smoke. It could cause an overheating event that could blow a coolant seal and then cause smoke, but it won't cause it directly.

About the only 'fault' the dealer could try to pin it on is if you show up with a stuck thermostat (an example) they, in theory, could say that the thermostat isn't covered, and so they won't cover anything else that failed as a result.

I've never known a dealer to do that, but then i know of very few cases where a warranty claim was attempted on just a cooling system failure

The other alternative is to just deal with it until it finally causes a compression loss, but that is hoping that it will get there before your warranty is up. But that can take a long time, given the engine design. When my cat failed around 55k, i'm positive it overstressed the engine and caused a coolant seal failure, but slight. I didn't fail a compression test until 96k....

 

Thanks again for the advice! Well from my research it seems that if I left the car to sit for a few weeks the coolant would corrode and destroy the internals of the motor.

How can I double check my thermostat now that you mention it? Just want to dot ALL my i's and cross ALL my t's!

 

The only real way to test each part of the cooling system is to remove it and test it outside of the car. Test coolant lines by running water through them, test the thermostat by putting it in a pot of water and use a thermometer to see what temperature it will start opening at, test the radiator by flowing lots of water through it and see if any junk or silt comes out if you flow backwards, etc...


I'd personally avoid replacing any of it before taking the car to the dealer unless it has an obvious failure, because remans tend to cause cooling system failures within 3,000 - 8,000 miles of installation, due to all the excess sealant used inside the remans on assembly. Breaks off in the coolant stream and clogs up stuff. I advocate driving the car as is during breakin, then do repeated coolant flushes (even with hose water if needed) to really flush the system thoroughly. And then replace at least the radiator and thermostat, if not everything (about $500 in parts from Mazmart) so that any junk caught up in those two will be removed from the car completely.

 

Cool.

Do you think I need to get my intermittent coolant level sensor taken care of before taking it in? Could they possibly blame that on overheating or anything and no longer cover the motor?

Or the rear O2 sensor error?

 

You probably need to replace the rear O2 before taking it in. They will not want to release the car back to you without fixing it, at a higher price than you need to pay. They shouldn't give you and problems about it in regards to the motor, but it would be better to eliminate that question.

No on the coolant bottle float problem, i don't see them giving you any problem over that.

 

Sounds good. That answers all of my questions. Thanks for being so helpful RIWWP

 

I had an engine fail due to a coolant seal failure... At first if I didn't drive it for a week or two it would flood and have a hard time cranking, but eventually it got so bad that every day it was having trouble starting after sitting even for 8 hours(overnight).

The way I finally figured out what was going on was by taking out the spark plugs(leading/bottom) and stuffing a paper towel near it while cranking with the fuel pump fuse removed. Basically the de-flooding procedure except knowing that gas wasn't in the engine.

Try letting the car sit for it's normal amount of problem time, and hopefully you'll see some results one way or the other. With my issue, I told the technicians at Mazda that, and they repeated the process to see the same issue, tons of coolant dumping out of the plug holes with the sparks removed.