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Discussion Starter #1
Hi All,

Long time lurker, I've found this community so great to get DIY information. I've been able to tackle a number of first time jobs myself: valve adjustment, new alternator, new radiator, compressor clutch, serpentine belt, idle tensioner, throttle position sensor, brake pads, rotors, trailer hitch, transmission cooler, brake controller.

In the last year the radiator failed, and the pink milkshake took out the transmission, a shop rebuilt it, and installed new engine mounts and steering rack & pinion.

2004 MDX at 190k miles, my hope is to keep it until 300k.
Shop installed Gates timing belt / water pump in 2014, 80k miles ago.


The current coolant problem came up when the cabin heat became intermittent on a long cold winter drive. At home I found the radiator was nearly empty, I was surprised because the engine temperature never indicated it overheated. I wasn't seeing fluid under the car but found the radiator cap gasket was bad and replaced it hoping that was the problem, but fluid was still lowering.

Under the car was pretty gunky so I cleaned it hoping to see if there was a visible leak and this seemed to make things worse. Now when the engine is running blue liquid is visibly dripping from around the timing belt cover. After short drives there is also white steam coming from this area, and the belt is squealing. (I assume the fan is blowing coolant onto the belt and its evaporating off the hot engine)

I'm keep topping up the coolant, it's been 2 jugs over 4 tanks of gas. The engine temperature has never even gotten to halfway on the gauge.

My thought was coolant is leaking from the gasket of the water pump, maybe the gates replacement wasn't the best.

However I also see blue/green coolant residue on the transmission side of the engine under the water passage and I believe on the side of the transmission underneath.

So then I thought maybe this was a head gasket leak? I checked the oil and it appears normal, under the oil cap, radiator & overflow appear normal. I checked for oil on the spark plugs but they were dry. I don't see any white smoke in the exhaust, and when the engine runs with no radiator cap there are no bubbles coming up. Should I get an exhaust gas test for radiator to confirm or rule this out?

I found posts that sometimes MDX water passage gaskets can go bad and leak, maybe that is causing the fluid to leak on top then drip down both sides?

I've attached pictures, maybe someone has seen this before and can give me some armchair advice?

What are the next steps? or estimated costs? Replace timing belt/pump? I think I could manage the job this time, maybe even a head gasket replacement. Or should I take it to a shop to diagnose/repair it if the problem is more serious?


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Under water passage

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Sure looks like it's a water pump (with the antifreeze showing up on the front of the engine). I'd go over anything in the area that could also be leaking AF just to be sure, but would start planning for another timing belt / water pump swap. The timing belt won't be helped by living in a constant bath of hot antifreeze... (and needless to say, you REALLY don't want a failure in the belt, or even one of the tensioner pulleys, which also don't like being drenched in AF).

And though it might (or might not) be unlikely, it's always possible that the shop skipped the step of actually replacing the water pump (make sure it really IS a Gates when you pull it this time).

I've heard nothing but good about the Aisin timing belt kits. That's what I put in my own MDX - drove it for a lot of miles (80,000?) afterward with no issues at all.

And finally - yeah, no reason to think that a well-maintained MDX can't make 400,000 miles. Mine was the most reliable vehicle I ever owned (something I miss when I'm laying under my BMW 530xiT looking for the new problem). ;-)
 

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Discussion Starter #3
Habby thanks for the reply! Did you part ways with your MDX?

Good point about the coolant being bad on the timing belt, even if it's not the source, given the mileage I should just bite the bullet and commit to doing the timing belt/pump as part of this fix. I've read many positive comments about the Aisin kit so I'll get that one.

I think the smaller leak of coolant on the driver's side is what's throwing me off. Do you think it's possible the water pump is leaking on passenger side and the water passage or head gasket or something else is leaking on drivers side at the same time?

I was considering buying a borescope camera that I could fish around the engine to get a better look.
 

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Yeah, I downsized to a wagon when I no longer really needed a 7-passenger vehicle (I do a lot of LONG road trips, and the gas savings are significant).

And yes, you're close enough to the "normal TB replacement" mileage that it's really not a big deal to do it now.

Coolant leaks can be funny things - sometimes they're coming from somewhere you REALLY don't expect - you might have a pin hole in a hose, for example (I had one of those that cost me a couple alternators in a car long, long ago). I can't really make out exactly where the driver's side leak might be originating... you might want to clean up any hint of the leak, and wait for it to reappear - sometimes the source will be more obvious that way.
 

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Late to this post but a few comments in case helpful.

For the coolant leaks on the driver’s side, there is the radiator hose connection to the T stat housing on the block and water passages on the driver’s side. The housing can rust out. If the mech replaced the T stat with the radiator, it may have come loose.

The water passages from the front to rear heads have been known to leak at the gasket at the front head. There is a cross over pipe under the intake manifold - you could take a flashlight and check for puddles between the intake manifold plenums.

The hose clamps on your main radiator hoses could need tightening or if they were not replaced, they could be cracked or swelled and then leaking.

Sometimes the coolant only leaks when the system warms up and pressurizes so you might check then but be safe and cautious.

(That the system didn’t tell you it was hot can be explained by that if you let the coolant get too low, the coolant won’t contact the temp sensor and register. However, often a tell tale sign is you’ll hear gurgling when you start up in the morning as air bubbles pass through the heater hoses in the passenger compartment.)

Good luck!
 

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LOP's advice is spot-on. I'd add that another sure sign of low coolant is when the heat stops working correctly, and you're blowing only warm(ish) air with the temperature cranked all the way up.
 

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Discussion Starter #7
Thanks for the feedback Habby & LOP.

The parts I ordered to do the timing belt job arrived today, so I got started. I got the crankshaft bolt out, drive belt, pulleys and covers.

The first thing I found was large blue crystal deposits inside the timing belt area from the leaking coolant:

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There is also some oil residue above the crankshaft, you can see it in the middle of the photo, any ideas what this indicates? I thought maybe the crankshaft seal was due for a replacement, but the oil is above it :unsure:

I borrowed a radiator pressure tester kit, to help me find the source of the leak, but when I pressurize the system the coolant doesn't appear to be coming from the side under the water pump as I would have guessed. Its slowly running down the front side of the engine block and across the bottom of the oil pan, it's about 1 drip/second so it's hard to tell its exact source yet:

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The good news is I'm not seeing any new coolant near the driver's side, though I'm still planning to replace the gaskets, o-rings & thermostat.

Next step will be to get the engine mount, timing belt, and water pump off. Maybe that will help me find the source, but any more feedback / tips are always appreciated!

Thanks
 

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Nice you were able to find those streaks and for getting a test kit.

Those blues streaks at the pump are a good indication that the pump is leaking somewhere - at the shaft or could be the joint between the block and pump body. There's a formed, o-ring style gasket around the perimeter of the body. It could get pinched or the pump or block can pit if regular tap water was used to fill/refill the cooling system. If it pits near the gasket, there isn't a lot of metal making up the joint. When you replace the pump check the area for pitting - if you find some, you might have to use an RTV type gasket sealer along with the o-ring.

That you find drips at the oil pan is probably because the coolant runs down and out the slot at the lower right corner of your first picture. It's a weep hole for drainage and it also lets you know if you have an oil or coolant leak. You can pressure test again before you button up the timing belt area.

If the coolant wasn't changed for awhile or was contaminated, those oily looking streaks could be from when the water pump was last changed and the mech didn't wipe or wash the area down. (When you pull the pump, about a qt of coolant could still spill out. The pump is lower than the t-stat which is about all you can drain to via the radiator. For a mech, just pulling the pump is also a faster than waiting to drain the radiator. It's takes more coolant to refill too if the radiator is drained. Anyway, a large pan is helpful in controlling the spill.) Then again, oil could leak from your cam seals so when you remove the belt, check behind and around the cam gears.

That you had coolant residue on the top side suggests there is a leak up there too.

Couple tips for refilling: make sure you run both front and back heaters max hot to fill the heater cores with coolant. I like to squeeze the heater and main hoses to burp as much air out as possible. Fill the overflow tank to the max line. Check the coolant level in the rad and overflow tank for a few days when the engine is cold and refill as needed.

After you are confirmed to be completely full but still lacking hot air, there is a heater valve that may be stuck or have a broken control wire. It's behind the engine, about level with the head, passenger side. You should be able to follow the heater hose. If you have a helper adjust the temp up and down, you should see the control wire turning an arm on the valve.

Good luck!
 

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You definitely want to chase down that coolant leak. Sometimes you end up just having to feel around "blind" in the areas you suspect until you come up with wet fingers. There really aren't a lot of shortcuts when you're looking for the source of the leak(s)… just find out where it is, then keep tracing it up until there's no more sign of a leak, and you've found it.

I'm hoping that the coolant isn't oozing out from the head gasket. At any rate, the pressure test kit is going to be your best friend through this process.

The same philosophy applies in looking for the source of that oil leak, too... it appears to be starting at that "top bolt", but I suppose it could just be dripping onto it from above, too...
 

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Discussion Starter #10
Looking at other posts/youtube instructions on the timing belt it definitely appears the inside of my timing belt is a mess, other jobs look silver and shiny, not good for mine.

I took the engine mount off and did another pressure test, coolant was clearly leaking out all around the water pump, and it still flowed down the oil pan so this could be the source I originally saw.

When I pulled the water pump off (that was a wet messy situation) I found the entire seal was glued in with another white sealant, take a look:

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The black seal broke and feels hard and stiff.

As I said 80k miles ago a shop previously replaced the TB, is glueing it in normal? Is it possible they didn't replace the water pump at all and just glued the old gasket back in?

Thanks again for all the help
 

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I have the MDX from HELL, so I can help on this one lol. If the gasket is stiff enough to break it has not been replaced in quite some time. All the gaskets on the front of the engine are HUGE weak spots and ALL of them should be replaced when the timing belt is replaced which is normally around 100,000 miles. The aftermarket kits are fairly cheap and come with all the parts to replace everything. If you haven't experienced it yet, at some point you'll wind up with an oil leak in the exact same places as your coolant leak and you'll need to rehouse your oil pump and oil pan. You might as well do it now while you have the front end apart
 

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When I did mine at the required interval, my WP gasket was still rubber like, not hard; twice now. Also no gasket sealant. It is possible the your WP was removed inspected and reinstalled with the sealant.
 

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I did the work myself. I bought an aftermarket timing kit that came with a new water pump, so I pulled the old one off and installed the new one. You are correct in that you should not use any sealant on anything on an MDX that has a gasket. If it keeps leaking again and again my thought would be that that water pump itself may be damaged, you're not torquing it down to the correct psi, or you're not tightening the pump down evenly. A new water pump costs between $35-$45, try replacing everything (the pump, the bolts, and the gasket) and put it together carefully and I'll bet it won't leak again.
 

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Jordan, just take a look to see if the water pump is a Honda pump, or a Gates pump (assuming the Gates kit comes with a Gates pump). If not, you might want to have a heart-to-heart with the shop that did the timing belt job last time!!!
 

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Discussion Starter #15
Thanks everyone.

Partial update
It took a while, but I carefully scraped off the old sealant with plastic scrapers & brushes so it wouldn't gouge and cleaned it all up.

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I fitted the new Aisin water pump on and completed another radiator pressure test and can report no water leaks at all!!

However the pressure gauge showed it was very slowly falling, is this still a sign of a leak? Does the rad have to keep perfectly sealed pressure forever or is a slow decline acceptable? Without any visible leaks I'm not sure how to track down the slow pressure loss.


Habby I can't see any markings on the old water pump other than a laser dot serial number, I wonder if there is some other physical indication if it was gates or OEM.
 

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Hard to say - I looked up the Gates TB kit, but the photo of the pump was awfully small. The water pump itself should look like the one in the link below - or at least I think it should (I'm assuming it's the same pump that they use in their TB kit, which would make a whole lotta sense, and that it hasn't changed, which is an assumption, though I'd bet it's a good one).

https://www.rockauto.com/en/moreinfo.php?pk=3096606&cc=1429118&jsn=8525
 

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I’ve got a spare of the same Gates pump and it has raised numbers and an ink stamp that says “Gates” on the pulley side near the tensioner mount. It’s fuzzy but you can see it in the Rockauto picture.

Your block cleaned up real nice!

If there’s no pits in the pump or block and if the sealant was only on the outside perimeter, seems the mech took the easy way out to try and fix a leak. If the sealant was in the grooves but still no pits, it may have been added as a precaution but have a hard time believing the gasket would be hard after 80K.

That you lose pressure might mean your leaking on the top side or could be your radiator cap is weak. (Hopefully not the head. You mentioned no signs of water in the oil). Did you get a chance to check the top and rad cap?

Nice work so far.
 

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Discussion Starter #18
I did another pressure test, turned off the humming fluorescent lights and put my ear to the pressure tester and I could hear a slight rice crispy snap-crackle-pop coming from it. I'm pretty sure that's where the pressure leak is coming from. It feels like it's on very tight, but its a used kit that's taken a beating. Hopefully my new radiator cap seals better.

I feel better about the pressure leak, so onward with reassembly.


The extra sealant added to the old pump was right on top of the existing gasket channel, it slipped over the edges and even into the bolt holes. Seems like a sloppy job. I really wish I did the first timing belt job myself now.

LOP, here is a picture of the old pump, there is no marking on the left side, just the "5957" and "A16115" I don't see any "gates" or other marking on it. I found a picture of the OEM honda pump and it has "Honda" stamped into it, so it's not that an original either, very strange.


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