Hi Everyone,
I have a 2008 RDX with 150K on the odometer and I'm having a litany of issues that I don't have any idea how to diagnose. The first symptom is the Check Emissions System light. I read around this forum and while others have had this light show up, I haven't seen anyone have it in conjunction with the burning coolant smell. When I first start the car, I can smell coolant burning (smells sweet). Twice now I've had to top off the coolant level, so I'm losing some somewhere. I can't see any leaks anywhere, radiator cap is good, hoses are all fine. Are these two issues related? I don't know where to start. Help!

Side note: I have no mods. The car is completely stock.

Thanks in advance!
Greg

 

you'll need to figure out where the coolant is going.
any white smoke coming out of tail pipes? have you changed your oil? is oil milky?

 

Sounds like you might have two different issues with check engine and coolant smell. I don't know if the RDX water pump has the drain valve that lets coolant leak before it starts to fail? I've had an 97 Honda Accord that had a bad radiator cap and coolant would evaporate around the cap instead of filling the overflow reservoir when the car got to operating temp. Had the plastic radiator develop a crack on the same Honda Accord that slowly leaked coolant. Those are the best case scenario. Back in those days, you needed to change the coolant more often and you would get a dry white crusty buildup (looked like hard-water build up) along with the smell of coolant. I haven't had any radiator issues with my 3 Acuras with almost 400,000 miles between them on +11 years. The newer coolant +100,000 formula might not leave a build up like the old school stuff. It could also be the heater core for the A/C system if everything else checks out.

Worst case is like justnspace said about white smoke from tail pipes or milky/cloudy engine oil which means your head gasket is leaking fluid into your engine. Could be much worst for the RDX since the engine oil also lubricates the turbo bearings. Don't want to damage the Turbo in the process of figuring out the issue.

They use to sell coolant dye you could put in the radiator and use a black light to find leaks. I don't know if they still have that at Autozone? Might be worth taking the RDX into the dealership to see if both problems are related and an estimate for repair. Might be $$ well spent if you know exactly the issues with the RDX so you can decide to sell or repair.

 

My oil change is up-to-date (although I did ignore it too long last time, roughly 5k miles overdue. I know, stupid). I pulled the dipstick yesterday and the color and consistency of the oil are good. Not milky, level is correct. No smoke from the exhaust at startup, but I haven't checked after running it for awhile. I'll do that after my evening commute today. Would I see it with a cold or hot engine?

 

That's a good idea, I'll try going to dye route to see what I can see. I'll take it as a good sign that the oil isn't milky and I don't see smoke from the exhaust. Hopefully it's something superficial and not too serious. I'd strongly prefer to to bring it by the dealer, but I will if I have to. There's also a very reputable repair shop near where I live who specializes in imports and gets excellent customer reviews. I'll probably take it by there first in hopes of saving some cash. They've sold me parts before at a fraction of what the other parts stores charge.

 

When you say you've had to top off twice, how much have you added and how often? (like twice in the last few months or twice over a long period) I ask because *some* coolant escape is normal for the RDX as the system is not completely sealed/pressurized. But, we're talking about ounces between oil changes, if that. I don't think I've ever had to add more than a cup to bring the overflow tank back between the lines. At your age/mileage I would definitely start with the water pump and see what comes up. If you can pull the actual error code from your emissions light, you can get a better idea of what's going on there. It may be listed in your diagnostic message screen within infotainment, otherwise use a code reader or Autozone.

 

if you checked the dipstick and it's a "normal consistency" then I would say the coolant isnt leaking into the oil, by the way of head gasket.
you will immediately notice a milky color once you have pulled the dipstick.

Mrgold had another idea of where it could go...it could leak through water pump.

 

I've had to add maybe a 1/4 bottle of pre-mix over the last month, so it's not an insignificant amount. Enough to have me worried about it. Guess I'll check the water pump.

I should also note that I had Autozone read the error code, and the guy said it threw up so many errors (plenty of which were for things that were obviously not wrong) that it must be a misreading. Which was super frustrating.

 

Weird for sure. I would agree that a quart of coolant over a month is an issue worth looking at. You can get a bluetooth OBD reader for under $20, and there are free apps out there (Torque for Android, not sure for i-Phone) that will connect and read your codes for you. May also be worth checking out.

 

Can you check to see if the radiator has any cracks/leaks/ dried up coolant anywhere? It could be seeping somewhere. Look for greenish/bluish residue.

 

Ok I bought an OBDII sensor on Amazon and the code is P0234 (Turbocharger/Supercharger 'A' Overboost Condition). So I have an issue with the turbo system, but I don't know if it's related to the coolant smell. I searched this forum for p0234 and found very little information for unmodified RDX owners. I'll continue to research that problem and see if I can solve it. Really trying to avoid going to the dealer for this.

 

Update: local shop pressure tested the cooling system and found no leaks or shortage of coolant. My OBD II sensor said the error code is a Turbo Overboost/Underboost code, and the shop said they can’t do anything with it and I have to take it to the dealer. So I’m back to square one.

 

Have you checked the transmission to make sure it isn't milky in color? I'm not 100% sure if the 5AT fluid runs inside the radiator to aid in cooling. If that checks out A-OK. I would lean towards maybe a bad radiator cap might be letting coolant leak/evap when the engine gets hot.

 

I wouldn’t know how to check that. I think I’m out of my depth here. I’m questioning whether I’m even smelling coolant or something else since their test came back fine. It’s strongest right at startup and it smells very sweet, almost like maple syrup.

 

Today I got a block testing kit from O’Reilly to check for head gasket leaks. The test came back negative but I do have white smoke/steam coming from the radiator (when the cap is off) and from the exhaust. Could that test produce a false negative?

 

Is the exhaust smoking / steaming only on first start or all the time? Any specific odors from the exhaust? Some puffs while warming up is normal - depending on weather it can be condensation burning off. A raspy burning smell with slight bluish tint can be oil burning, a while smoke with a very sweet smell can be coolant burning.

If I had to guess, and it's just a guess, it seems like you may be losing a very slight bit of coolant through your head gasket. Not enough to cause major issues, but it seems that it's enough to cause accelerated coolant loss in the reservoir. The the car is turned off, the coolant in the block may be seeping into the cylinders ever so slowly as to cause the white smoke and sweet smell on start up, but not constantly. I wonder if the head gasket is possibly failing, but not completely blown.

 

This is more of an FYI in progress coolant leak share.

My sons 2008 RDX 2.3L Tubo has a similar coolant leak which was producing a burning smell.
The both leaks were traced to the Exhaust manifold side of the engine (Between firewall and engine).

One leak was traced to a short 90 degree coolant hose between two 1/4" metal lines. This hose was only accessible from underneath the car, I had to remove an exhaust bracket attached to the engine block near the transmission and the exhaust pipe. It was either that or remove driver side axle to be able to get hand access, which I decided against. It was a tight squeeze even with the bracket removed, but possible to replace. The old hose had lost most of it's elasticity due to its oven like position below the Turbo and between the block and the exhaust pipe. Also the the faulty hose ha been leaking at one end and had deposited visually detectable layers of coolant on the metal line it was attached to.

The second leak hasn't been isolated to a specific hose yet, but is on the Exhaust manifold side, above the Turbo Intake tube in a cluster of emissions ans coolant hoses. I am planning on using a dye to locate this leak since it is in a very congested area of plumbing and brackets.
However, when monitoring the leak from under the vehicle, I can see it produces about one small drop per minute as it drips from above on to the exhaust manifold then down on to the exhaust pipe.
Even with an inspection camera it is impossible to snake it from either the top or the bottom, to be able to see the hose source. The leak has been occurring for awhile and does produce the burning smell. the cooked coolant can be seen as burned streaks on the exhaust heat shields. I can see with my inspection camera from above looking from the passenger side moist areas along the base of the valve cover head casting above the exhaust manifold ports, where the coolant has wicked along the cover for a while. Again there is ton of congestion with emissions, coolant and brackets, so I'm pretty sure this is a hose buried the congestion. Even with the dye I will have to methodically remove all the obstructions to uncover the source.

My sons car has the recommended Blue colored Acura coolant, so if there is a coolant leak this would be a clue. Basically if your just idling the car and the leak is present on the exhaust manifold side of the engine, there will typically be a burning smell, since the exhaust manifold, Turbo and exhaust system plumbing are dominating this side of the engine.

 

I'm updating me initial reply post to what I called my remaining leak of the two listed , I've determined that the remaining leak source, it is leaching up-wards from the exhaust manifold gasket which seals to the head around the cylinder 2 and 3 area.
Basically, I had to remove quite a bit of valve bypass plumbing, and initially the leak look like the o-ring on the exhaust manifold coolant outlet tube may be the source, but not till I finally removed the valve cover could I clean things up enough and perform a pressure test and finalize the position, now the work begins. I'm using a nice pressure tester loaner kit from Advance Auto, which has over a dozen adapters for many vehicles and pumping the system up to 15 PSI., which is with in the range and enough to exploit any leaks.

This is my sons rdx I mentioned in my first post there was a repair performed on another leak which was thought to be a water leak, this leak was diagnosed and repaired at service shop. However, before I tackled my diagnosis I downloaded many diagrams for this 2008 rdx and was able to determine that the first of the two leaks was not a coolant leak at all. It was oil return line from the turbo which has a small section of hose which was in fact leaking. The problem with the repair though was a coolant hose was used for the repair, which I was concerned is only designed to run at 15-16 PSI as oppose to an oil pressure hose which would be much greater, so I ordered the correct hose part from the Acura dealer and replaced it one more time.

Anyway I will update my DIY work as I learn more.

 

Hi,

I know this is old but wanted to see what your resolution was? I am having a similar issue with mine.

 

Be sure and check in the rear of the engine above the exhaust manifold, there's an o-ring that seals a coolant feed pipe into the exhaust manifold and this o-ring hardens over time due to age and high heat and begins to leak. I think what happens is the leaking coolant boils off because it's leaking onto the top of the exhaust manifold and you might not see the coolant reach the ground.

 

Thank you! The pipe on the video is the press fit one and on the opposite side, there is an o-ring but both of these are ok. Mine just has an issue internally at the moment, but no external leaks. This vehicle was purchased cheaply with a rusted out coolant pipe (big one under the intake) and a blown head gasket. Would run fine but the gasket was so bad that you could feel exhaust pulses through the radiator during startup. Replaced all of the obvious items, machined the head, went back with studs, and did some maintenance items. Now the car will run up to temperature before gasses begin entering the cooling system and coolant begins erupting all over the place.

Based on the state of the exhaust manifold, I do believe this is where the problem is. I did try some K-Seal yesterday and ran it up to temp with no overheating but have yet to drive it more than 10-feet. The OP had mentioned coolant wicking up around the manifold and I was curious about the manifold bypass that was mentioned. If I am still having issues, I may try bypassing it, at least for testing purposes. I am not sure if Honda's intention with this was to heat the water or cool the manifold, but the turbo has its own cooling separately. This is one of the only images I got during the build-up but you can see the corrosion on the manifold and some of the pitting near the bottom ports.

 

I


I think the coolant path to and through the aluminum exhaust manifold is to cool the aluminum and unfortunately there's a lot of potential areas for leaks. Your engine sounds like it may have overheated in the past so potential damage like warpage or cracks in the head and exhaust manifold. Did you check the mating surfaces between the head and exhaust manifold? It's a ton of work to change the exhaust manifold, as you know, and a new exhaust manifold cost over $500 too but may be worth if the original manifold is damaged beyond repair. Was hoping it was an external leak.

 

That is most likely the case unfortunately, and it may still receive coolant anyways up through the head. That is the part I am unsure about and wish I had further explored this while I had everything apart. There was another post on here where they were doing a performance build and welded all of the ports shut, but that was with a different head, bigger turbo, and likely a lot more heat. His ended up cracking internally but I am not sure if that would've happened on a normal daily with no mods. Another observation was that the 3 middle/rear head bolts were not as tight as all the others, but there was no evidence of anyone having been into it that far. This is one of the reasons I went back with studs.

I don't mind the labor to change it and now that I have done it once, I feel I could cut the time down substantially. I just cant justify paying 3/4 of what the car cost for a new one. I do have a second run up to temperature with the K-Seal and also finished with a 1500 RPM hold with no overheating yet. Actually stayed a couple of bars below middle. I hope to do some driving with it today but want to pressure wash first since it is still burning off fluids and such.

 

A leak down test could help pinpoint the leak to a cylinder and if it's a leak in the cylinder head or not.

 

I will try doing that if the issue persists. So far, I have run it to temp 3 times, with the 3rd time being a few drives around the neighborhood. All seems well except for stuff that is still burning off. Temp remained 2 bars under middle. This made me remember that after initially starting this up, I confirmed combustion gasses in the coolant, had steam from the tailpipe, but no running issues and no CEL. Another check in the box against the manifold I suppose.

I do still plan on just replacing that manifold, once I can source one from the u-pull yard.

 

Just a quick update. We have been driving this a lot more and have about 500-600 miles on it without further issues. I did find an exhaust manifold at the salvage yard for about $25. I will just hold onto it until it is needed, but so far so good. I have also replaced the front struts, rear shocks, front/rear links, tires, and I have treated the entire underbody since there was only surface rust currently.