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Discussion Starter · #1 ·
The last couple months I've been noticing the radiator coolant is very low, but the reservoir is full. This has me stumped? I did notice the small hose leading from the top of the rad, next to the cap and leading to the reservoir pooped off the rad. It's been very loose in the past, so I clamped it on. I've topped off the rad and turkey basted the reservoir to the right level. After a days drive, it's back to the issue I have. Any thoughts? I have notice an oil leak from the engine but it's everywhere underneath and hard to tell from where?

About a month before I noticed all this, the rad fan would run for a while after a drive. It's never done this. Finally I got around to checking the coolant level and found the current situation. I did have the engine rebuilt about 2.5 yrs ago, last summer I pulled the top half of the engine off, adjusted the valves, replaced a lot of seals, plugs, and all 6 packs. I also carb cleaned everything as I went along, obviously. The took apart and cleaned the EGR valve.
A few weeks ago when we had cold mornings, 50 here in Florida, at cold starts, the engine would shudder with low rpms until it warmed up a few minutes later. As it was running like this, the exhaust would make the same noise at the tailpipe, similar to when a pack is bad or when you disconnect one. Just adding this last part if it's a "tell" that I don't know about. Now that is has warmed up, it's not having this cold start issue.

I'm planning on replacing the EGR valve since the car has 240k miles and the cel codes are : P0300-6 and P0430. It also shows everything ready except "Evap not ready"? I just disconnected the battery and will see what codes come back. I'll post if they're any different....
 

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Might not be the same issue but symptoms seem similar - misfire on cold start, low radiator level. I was getting mainly P0305, occasionally P0300-P0306. Ended up being a blown head gasket on the front head. My post is in the 1st Gen section under, P0305, Blown Head Gasket? (A couple of my posts after the first ramble so skip those.) Its fixed and running well with over 700 miles now.

Three things that helped me narrow down cause. Discovered the spark plug for #5 wet but not oily wet. Wet like with water. Then used a inexpensive bore scope that I picked up on Amazon and looked in the cylinder through the spark plug hole and found water droplets. Then did a radiator test suggested by Bluepill and confirmed exhaust gas residuals in the radiator. For that test, rented the tester from Autozone and bought the test fluid for about $8. If you don’t have a bore scope, that might be the easiest, fastest, cheapest test to confirm a blown head gasket.

Good luck!
 

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Could be as simple as a bad radiator cap. It not only releases excess pressure, but also opens under vacuum to allow coolant from the overflow tank back into the radiator as the coolant cools down. Look at the rubber seal on the cap. If it has expanded and is distorted, or is damaged (Torn, etc.) it needs replacement.

You may also have a small seam leak in the radiator or a bad hose connection somewhere that does not allow vacuum to build up. Pressure testing the system is always a good idea.

You may still have a bad head gasket, but the cap is way cheaper.
 

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Discussion Starter · #5 ·
The radiator cap looks perfectly fine but I'll try swapping it out with a new one. The new EGR valve made no difference. But the way, this is the part I ordered from Amazon, https://www.amazon.com/gp/product/B000IYRHAY/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1 . Wells EGR4201 EGR Valve. All the Valves listed for the MDX had a smaller opening at the bottom. This one was just as large as the opening it bolts to. The valve I took off the car, which is original, had the smaller opening though. This confused me since you'd think the poem would have the larger matching opening. Any thoughts? I am sending it back for a refund, the male portion where the plug goes into, was cracked and pushed in. It broke off when I payed it open in order to plug in. It still plugged in fine and I don't see how it would effect function. It works out, I'm sending it back for arriving damaged and it didn't change any current issues, so I lucked out in that respect.

I forgot to mention in the original post, my mileage is horrible. I average 14mpg and there's noticeable power loss. If the rad cap makes no difference, which is what I'm expecting, I'm thinking of doing the head gasket myself. Last summer I did the valve job and the head gasket looks to be only one step further. I watched a video on it and I'm not comfortable with the timing belt aspect of it. Looks like the timing would have to be redone since the cam comes off with the head? Is this something where I can simply mark things and put back no problem, or does it need to be precisely done, which is what I think....? The head gasket is either putting in head gasket sealer or an actual gasket and sealer? Is this an pretty straight forward job? If I managed the valve job, then doing the head gaskets should be no problem? Any tips or things to change/complete once I'm in there? Like I said, I adjusted the valves, all gaskets, plugs, coils replaced and everything cleaned as I went along. Anything other than these that should be replaced going the further step on the head gasket job? If it's technical as when it comes to the timing aspect of the job, I might see if my mechanic might cut me a break if I bring the car over, tear it all apart, let him do the timing aspect of it, and then let me put it all back together. This will save me a bundle I don't have nor care to put into the car which just hit 240K. Although the engine was rebuilt 2 years ago. I'm surprised if it is the head gasket since it was rebuilt so recently.... I also need to replace the passenger side axle and half shaft, in hopes of ridding the car of its shudder/shaking when accelerating around 45mph on up, and cruising over 55mph. When I let off the gas, the shudder stops. It's only there when gas applied. I replaced the drivers axle last week and used my lifetime alignment at Tires Plus. I've gotten my money out of that purchase! I've kept my eyes open for a deal on another vehicle if the $$ adds up for all the needed work... I've got the shudder at accelerating, water leaking into he drivers footwell, recently the drivers A pillar now has a leak when it rains, heating on both seats not working, roaches has been residing in the car for about 2 years now due to the dampness and rain three messy boys in this car, and the clear coat is peeling on the front end and parts of the roof.... But I love how the MDX drives and feels when in perfect working order. I set poison pellets everywhere and spray when needed for the roaches or Demons as the kids call them!

As far as the missing coolant, where is it going? Is it evaporating from the engine heat? Is it leaking into the engine? I don't see or smell coolant in the oil/dipstick? Should I not drive it until I get the head gasket fixed or is it fine to drive? I don't want it to get to the point of no return by needlessly driving it.

I'm currently awaiting parts to repair the rear sway bar. About 1.5 years ago, I replaced the rear sway bar bushings. One of the bolts for the bracket on the passenger side snapped. So I simply tightened the remaining bolt and prayed. Well months later the bolt had it and flew the coup. So I ordered a new bushing, bracket, and bolt. I think I'm going to weld the bracket in where the bolt snapped off at. Otherwise it looks like the entire rear suspension/subframe will have to be dropped in order to drill out the bolt. Am I correct? I don't see any easy way to do it, other than welding. Permanent? Yes. Will It need replacing again? I hope I don't have it by that time.... Does anyone have an easy way around this which I'm missing?
 

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1. The shudder you describe is typical of a bad INNER CV joint on one or both of the axles. Easiest way to diagnose is to replace, unless you are experienced with axle disassembly and diagnosis.

2. Having a head gasket failure within 2 years of a proper rebuild sounds like poor work or bad parts. These engines are very complex and high tech, and many mechanics who have been successful with earlier technology come to grief with the 21st century stuff.

3. If the radiator cap does not cure the loss of coolant problem, next step is to test for combustion gasses in the radiator. Lots of youtube videos available.

4. Just replacing the head gasket is no assurance against a repeat failure. If the engine block or the head is warped, a new gasket will fail again. The surfaces have to be carefully inspected for cracks and flatness.
 

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Well, at 240K miles and all the problems mentioned, you said it yourself, you got your money's worth!

Probably not worth fixing the driveline or anything else until you get your engine resolved. You'll have a shudder-free car that runs like crap. And then you'll still have the leaking, peeling paint, and a no seat heater car that might start to smell musty.

Probably worth investigating if the engine can be saved with less than a head gasket and related work. I followed Bluepill's advice and it was spot on. If you haven't already, pull the plugs because they can tell a story. You mentioned you adjusted the valves. How long ago? Have you checked them for this current problem because incorrect valve clearance can result in misfires. The front valves are easy to get to so you can check those relatively easily and see if that might be the problem.

If you're careful and patient enough to adjust valves, you can probably handle a timing belt uninstall and reinstall to remove the head. I found the hardest part is taking off the crank pulley bolt. There's a lot of parts to remove. The belt itself is about careful alignment and after install, turning the engine by hand with the pulley bolt to make sure the timing marks on the crank and cams align. You can mark the position of belt and pulleys with nail polish but I would not rely only on that.

IMHO, if the engine is more work than a few hours and a couple hundred bucks, it's time to let it go. I've kept my cars for 230K, 240K, 260K miles (a couple were still running good) and its always hard to let them go. However, as soon as I get the replacement, the old car is just a good memory that's soon forgotten. You could put your time and DIY experience into the next car.

Sometimes you get to make the tough call. Let us know how it goes, what you decided. Good luck!
 

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Are you still having the loss of coolant issue with no signs of external leaking?

Also is the misfire codes still coming up? If so what are they?

I have a easy and accurate procedure you can do to check for a head gasket problem.

Let me know
 

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Discussion Starter · #9 ·
Well I replaced the rad cap to no avail, not surprised. I called my mechanic who rebuilt the engine and he would be shocked if it was the head gasket. He replaced everything with new quality parts, and is confident that's not the issue, especially within 2 years. I put in a green dye which he suggested and to search for leaks with a black/uv light. Yesterday I did find where the leak is ending up, behind the passenger front tire. Under the car, area where the body and front of the passenger front door meet, but a few inches away from the edge of the car. There's the green coolant. It looks like it's seeping from inside the car, between the panel welds. You can see a tiny bit coming from the bottom rear of the back of the passenger front fender well. I'm guessing the heater core is leaking? I don't see any type of leaking from the control valve and hoses in the engine bay at the passenger side firewall, so it must be from inside the car, behind the firewall? I haven't checked for loss of heat since we live in Florida. We might use the heater couple times a year.
I have checked under the passenger side carpeting, but it looks just like the drivers side, due to the leaking we all get. Damp, slight surface rust, but no sign of the dyed coolant though. So I'm confused at this point? What now? Do I tear apart the dash/glovebox? What am I looking for? Could it simply be leaking hoses which I need to tighten or replace? From what I do know of heater cores, they're a nightmare to replace, and there's no room to work with. I haven't found anyone else with the issue I'm having. The only thing which comes up, is the tightening of the valve phillips screw in the engine bay at the firewall, but not my issue.
By the way, the codes that pop up are the usual P0300-6, and it shows that the Evap is not ready. Any ideas? Mileage is still horrible, 14mpg city, and there's a noticeable loss of power. I know you guys have given good advice on things to try and I haven't done everything. With my bad back and pain, There are bad days and worse days. So I can only try what my back and attitude from the pain allow. Please don't think that I'm blowing off any suggestions.....
 

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Hmm, slow leaking coolant like you think it is still wouldn't cause a random misfire code.

Is there a certain cylinder that misfires the most? Like which misfire codes comes up first other than the random misfire code?

Are you sure coolant is actually leaking externally and not internally?

You need to do a internal leak test. Do you own a little round mirror that fits and seals over the spark plug hole?
 

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Discussion Starter · #11 ·
Yesterday I took the car to a mechanic next to my barbers, he owns the building and used to run the shop as well. The mechanic seems very cool and honest. He gave me a bunch of scrap to haul away last month and it turns out he had a set of heads from an Odyssey that he already had shaven but ended up not using in the pile I scrapped. He works on a lot of Hondas. Using a scope, he found coolant in one of the rear pistons. So the head gasket is leaking. He also determined that 2 of the coils I replaced last August were bad, causing the misfires. So I already bought another set and will just return these. They have a lifetime warranty and I'll just get a refund for the ones I just bought, vs. taking mine out, getting a ride to Autozone to swap them out. They're Duralast, and with my mileage, I have no problem swapping them out with the warranty when they go bad. I now know the signs....
I'll try to replace the head gasket myself next week and take the head to be shaved to a local shop recommended by Oreilly's. The mechanic still has the head gasket from the Odyssey that he offered to give me when I tackle the job. I'm surprised the head gasket went out so soon? It's only been 2 1/2 years since the rebuild, and the engine's never overheated. The needle never moves!
Once that's done and she drives fine, I'll then swap out the passenger side axle and half shaft, hopefully getting rid of the wobble/vibration issue it's having.

Well this has all been good news and bad news. I was looking for another vehicle, which we currently can't afford but I was looking forward to driving something else after 13 years. No matter what we do eventually get, it won't be as nice as the MDX though. It's old but still a very nice car. I did find a 2004 Volvo V70, drove it and everything checked out, but ultimately it was just too small for out family of five. The three boys would be shoulder to shoulder in the back seat, and that just wouldn't work for my sanity once they start fighting....

I'll post again once I get the head gasket replaced and report on how she runs. By the way, once inside, I'll recheck the valves again and replace the spark plug tube seals too. They've ripped again and the tubes are full of oil again! Does anyone know of any seals that are stronger than what Rock Auto sells? Are OEM any better or just the same? They were tearing as I was replacing them! So I'm not surprised.... I'm thinking maybe aftermarket seals are garbage since the ones I used last August tore as well as the ones used in the rebuild 2 1/2 years ago. Is it possible oil in the tubes can cause the coils to go bad? The stock ones went bad after the rebuild, when I found oil in the tubes and the coils I put in last August are going bad as well now that there's oil in the tubes once again! I think I'll order OEM seals this time unless someone knows of anything stronger/better made?
 
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