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I'm just about at my wit's end with this issue. This vehicle belongs to my mother, it's been a very reliable car, but of course it's 23 years old with nearly 200k mi on it. Original engine and transmission (still shifting great). Last year I received a complaint about the heater intermittently blowing hot. I diagnosed the issue quickly as low coolant + air in the system. The 1st found leak was at the water pump and thermostat seals, this is where things started. To keep this as brief as possible, here's a list of repairs I have done since this problem was 1st discovered. (Note: This issue was discovered quickly during the winter months of 2023, to my knowledge, the engine never overheated due to low coolant).
1) Replaced Waterpump and timing set, including new OEM thermostat + seals. (Also replaced spark plugs, valve cover gaskets, and rear cylinder head plugs).
2) After timing/water pump & valve cover jobs, observed coolant level still dropping at overflow reservoir. After pressure testing, discovered leak at back of cylinder head coolant outlet (RTV gasket failed). Cleaned up and re-sealed with Hondabond, no more leaks observed after repair. Also replaced the radiator cap with a new OEM unit.
3) Observed coolant level in overflow reservoir STILL slowly dropping. Inspected block drain pipe (didn't know about this until recently), rubber cap & clamp are good (no leaks), but seal at the block was seeping. Replaced O-ring seal and used Hondabond for insurance (no leaks observed after repair). I also replaced the radiator with new Koyo unit and installed new OEM radiator hoses. Old radiator & hoses were not leaking, but the radiator was 10+ years old and the hoses looked to be original.
4) I am STILL observing very slow coolant loss at the overflow reservoir.
Other Notes:
I have pressure tested the coolant system and inspected all the common leak failure points, such as the heater core valve and hoses, thermostat/water pump. I am not witnessing any drips or seepage at any of the rear coolant hoses/fittings. The interior does not have a antifreeze odor from the vents nor does there appear to be any dampness in the carpet or fog/condensation forming on the glass. The car fires up and runs like a swiss watch every morning (cold start). There is no coolant mixing with oil, there is no white smoke out the tail pipe. I sincerely doubt a head gasket issue.
Final Thoughts:
At this point, I suspect there might be coolant seeping from one of the O-ring seals for the cylinder head crossover pipe (hard pipe in front of intake manifold, runs overtop & connects to thermostat housing). Outside of this, the only other thing I can think of would be the heater core. But as I stated at the beginning, I'm nearly ready to give up on finding the source of the seepage. Aside from the green crusties & drips in evidence for the previous 3 leaks I repaired, I cannot find any other witness/water marks. The coolant loss rate is extremely low after the repairs. It's 1mm or less difference (drop) per day. Coolant top offs would need to be done at least once per month at this current rate. This is a CA vehicle, so there's no rust & corrosion. When I 1st flushed the radiator coolant, it was clean, no signs of corrosion or combustion gases mixing with the coolant. When I replaced the radiator hoses, there was no signs of pipe cancer either.
Things I'm thinking about trying next are...
1) UV dye in the coolant. I have a black light already that I've used for detecting AC leaks. If the heater core is seeping, I can check the condensate drain water for signs of a leak.
2) Replace cylinder head crossover pipe seals, somewhat big job, requires the intake manifold to be removed and gaskets replaced. This is one area I haven't been able to inspect closely.
3) Replace heater valve anyway, even though I cannot verify or detect a leak there. The valve appears to be original and I know these are prone to fail.
But what are your thoughts & suggestions? I'm hoping there's a die-hard RL fan or Honda/Acura Tech on here that has experience with these older 1st Gen RLs with the C35 engine. I don't want to let something minor like this be cause to junk the car (which is what my siblings want to do!). It still runs like a top, interior is in great shape, very comfortable, well maintained. Only issues the car has are cosmetic (exterior paint fade, dings, etc.)
Are you checking the coolant overflow tank after the same drive or at different times? The level in the overflow is supposed to go up and down depending on temperature of the radiato. if it's completely going down and not coming back then it's a problem but want to rule out user error in testing
Yes. I’m familiar with how an overflow works to handle expansion and contraction with heat cycles. I’m checking the level on the vehicle in the morning, completely cold engine (sitting over 10hrs without use), on level ground, same parking spot each day. Otherwise, to your point, you won’t get an accurate measurement.
I also forgot to mention that I bled the system properly using the bleeder valve at the top of the coolant crossover hard pipe and using a spill free funnel. I ran the engine for about 30min with heater on full blast and blipped the throttle periodically to ensure trapped air was purged.
The heater works great, thermostat is opening/closing properly. No foam or bubbling action observed at overflow.
Cheers!
-Icer
Man, I'm at a loss as well then.. UV dye might be a good next step but there is clearly a leak if the level is dropping... any chance coolant is falling onto the exhaust manifold/jpipe/catalytic converter and just evaporating thus not hitting the floor? It's clearly going SOMEWHERE
I had the same thought as well. In the case of the REAR WATER OUTLET, the coolant was indeed dripping onto the back of the engine right next to the exhaust piping and cooking off before it ever dripped onto the ground. Because of the prior oil leak at the rear cylinder plugs, this leak was easily overlooked as the coolant was mixing with the oil. I only discovered this leak using my pressure tester, in this case, I was able to get drips to form at the bottom of the sealing surface.
Here's a diagram of the upper engine cooling system. The one area I haven't been able to check closely has been the piping and O-rings in the valley between the cylinder banks. The coolant plumbing here all lives under the throttle body and intake plenum.
There are 3x O-ring seals that I suspect might be seeping. These seals are components of the WATER BYPASS PIPE, CONNECTING PIPE, WATER PASSAGE, and THERMOSTAT HOUSING ASSEMBLY. I would need to remove the WATER PASSAGE PIPE (what I've been referring to as the cylinder head crossover pipe) to gain access, however this pipe seals to the cylinder heads using the same gasket as the intake manifold. Honda/Acura recommends replacing the gasket, but sometimes you can simply re-use the gasket if it's metal. I really don't want to remove the entire intake manifold if it's not necessary, but I also don't want to fix one leak only to cause another.
Does anyone know what material these intake manifold gaskets are made of? Are they truly one-time use?
Can the intake manifold be removed without splitting the clamshell and removing the throttle body?
https://www.rockauto.com/en/catalog/...ld+gasket,5400
unfortunately I’m not too familiar with the older C35 engine but on the J35, i often reuse the gasket as it is metal. it look metal here as well versus paper which ive seen on the throttle body/Intake manifold mating surface.
Looks like Honda/Acura discontinued one of the intake manifold gaskets. I do see a full Fel-Pro set though and the inner diameter sealing surface appears to be rubberized, so these are probably one-time use on the C35. Given the condition of the block drain pipe O-ring, I'm sure most of the rubber O-rings are shot (hardened up). I already have OEM O-rings for the pipes. I guess I'll just get the Fel-Pro complete upper intake set (just in case) since it's super cheap and includes more than I should need. I'm really hoping I don't have a problem with the heater core. Ripping apart the dash on this car would be an absolute PITA.
Cheers!
-Icer
Btw, the C35 is an absolute bear to work on. This is late 80s - early 90s tech, no VTEC, tons of vacuum lines all over the place mixed in with electro-mechanical sensors. The engine (bottom and top end) mechanically speaking is very reliable/solid, just in that weird time period where the last of the 80s technology was clinging on before being completely dropped for full electronic controlled ignition systems. This guy still uses a cable actuated throttle body and variable length runners. It's a 90* V6 with a balancer shaft, which is unheard of today. I have a love/hate relationship with it. I love that it's actually still running great, but I hate how much crap you have to disconnect and remove to do what should be, simple repairs/maintenance.
Cheers!
-Icer
Weird as it sounds, I'd try to tighten the overflow cap when the car is hot. I find that they expand as the engine gets hot and allows coolant to evaporate slowly. This worked for my 14' RLX as it was losing small amounts of coolant on a consistent basis. Once I tightened the cap, it stopped losing coolant. Just be careful not to strip it obviously. Curious to hear specifically what is hard to work on with this car. This car is simple for me to work on at least. Haven't done any major repairs though except for the timing belt. That wasn't too bad though.
Last edited by 1186KA9; 03-27-2024 at 02:55 PM.
Reason: fixing bad spelling
I'll give the reservoir cap a second look over, but I didn't notice any residue around the cap or threads, been keeping it pretty tight (for a plastic cap at least).
You're right about the timing belt job, that really wasn't all that difficult, you don't even need to remove the fan package to gain access to everything. But doing the valve cover seals was not fun, with so many vacuum lines running overtop the engine, this job becomes a real pain. To gain access to the valve cover bolts on the driver side, you need to pull out the battery followed by the the cruise control actuator and fuse box (if I remember correctly). Just lots of little items that are a hassle for a simple valve cover gasket job....which on this car isn't simple at all. On the bright side, at least the engine isn't transverse mounted like most J35s.
Another bear of a job was resealing the rear coolant pipe on the back of the driver's side cylinder head. There's a mess of brackets and hoses there that are an absolute pain to work around or remove. One of which was the transmission dipstick tube.
In short, even though this is a large engine bay, because the C35 is a 90* V6, most of that space is eaten up, making access to fasteners for certain jobs a real pain. It doesn't help either that all the plastic and many of the hoses have become brittle from age and heat cycles, so you can't rush through any of this work, you really need to be careful with every hose and wire harness connector.
Cheers!
-Icer
Huh. Off memory, I never removed the fuse box or cruise control actuator for the valve cover gasket. I only had to remove the 3 vacuum lines on the right side of the engine. That wasn't too bad. Space isn't that great, but its not too bad at least for me.
Is it 100% necessary to loosen up the fusebox & tuck it out of the way? No, it's not, but it makes the valve cover removal and installation a lot easier. The reason for the removal is to give better angle/access to one of the lower cover fasteners (next to the shock tower support). You could probably sneak in there with an extension and u-joint, but this could lead to other headaches like stripping the fastener. I'll admit, I'm not well versed in all the subtle changes over the years of these cars, perhaps yours being a newer production year (2004) has some changes to the engine bay arrangement.
I received the Fel-Pro gasket set from RockAuto. I have some other car maintenance projects scheduled for the coming weeks, but I'll post my findings to this thread once I've had a chance to investigate and complete the work on the 01 RL.
Cheers!
-Icer
Been busy wrenching on other family vehicles amongst my own. Two days ago I put UV Dye in the RL's coolant system as a visual aide and confirmation on the leak. I'll be inspecting the vehicle come Monday with my Black Light, I'm hoping this sheds some light on the issue (literally). I have the gasket set ready to go, just need to schedule the time to work on the car. I'm suspicious of the overflow hose and heater core valve, I want to rule those out before tearing apart the intake manifold.
Cheers!
-Icer
I have an oo that had the same prob but is was a head gasket leak the car had overheated however it could be one of the underhoses you mentioned but given the cars age its best to replace them all I love working on the car right now it has a major misfire nut somewhere is leaking on the intake manifold as i made a smoke machine to test it and the smoke is coming from the intake manifold . but it drives superlatively now the gaskets are done
I really hope it's not the head gaskets, none of the tell tale signs are there, but if the leak was small enough, it's a possibility.
Around the time I created this thread, I discovered some carbon/sludge (gritty, sooty, tar-like) build up in the crankcase. It was on the dipstick and under the oil fill cap. I quickly diagnosed this as a PCV system malfunction as the oil is regularly changed on this car. In fact the oil had just been changed a week or two prior when I discovered the sludge. The root cause of the problem? It was the PCV hose that runs from the PCV valve on driver's side valve cover, over to the intake manifold. The hose was collapsing under vacuum simply due to age. The rubber had failed and could no longer maintain it's shape. Sadly, Honda no longer makes that nice pre-formed PCV hose, I had to get some universal vacuum hose and put in a patch. Afterwards I ran some flush through the engine and topped off with fresh oil just for good measure. I haven't seen any new sludge build up, but I'm recommending early oil changes for the next 3-4 cycles to help remove the contaminants.
It just goes to show that you need to pay attention to the rubber hoses on these, they're 20+ years old and at their limits. If they don't outright rip, crack, and break, they might collapse like the PCV hose. I suspect your intake manifold leak is related.
Cheers!
-Icer
Update: Looked over the car last night with my black light (as thoroughly as I could). Unfortunately, no smoking gun evidence of leaks at the reservoir bottle/hose, radiator and hoses, heater core valve, or any other coolant lines easily visible/accessible at the front, top, or back of engine. I also checked the garage floor under the car where the AC condensate drains & pools. No signs of UV dye there, so that's good, doesn't appear that I'll be needing to rip apart the dash for the heater core. But I will need to schedule the work for removing the intake manifold and replacing those gaskets and O-ring seals. If that doesn't resolve the issue, then it's possible the headgasket(s) are compromised. Before I dig into the intake, I'll have a look with my endoscope into each cylinder, if any of them look "steam" cleaned, I think I will have found the answer.
Cheers!
-Icer
The piston tops might have carbon deposits that hot coolant can't penetrate so it might not be definitive, i am guessing its gonna be the head gaskets be prepared to machine the heads as well wont make sense to just change the gasket once youre in there
Yes, if it comes to that, but I'll cross that bridge when I get there. The coolant loss is minor at this point and performance hasn't been impacted. The labor/time to pull the heads and have a machine shop give them a refresh would probably outweigh the value of the car. A gal or two of coolant per year isn't that big of a price to pay to keep it road worthy (top off reservoir every 2-4 weeks).
Cheers!
-Icer
03-26-2024, 02:55 PM
