Mishimoto radiator drain plug leak

[BD40]

2 Mishimoto X-Line radiators and 2 leaky drain plugs. Mishimoto sent new O-rings and then a new radiator because first one dripped like a leaky faucet. Now the second one is dripping after 18 months and 1,500 mi. I've tried to follow Mishimoto's directions to tighten the plug finger tight plus 1/4 turn. But, even finger tight causes the O-ring to squeeze out and leak. So, finger tight plus 1/4 turn seems out of the question. The threads on the plug are very loose (sloppy) and Teflon thread tape doesn't work. What am I doing wrong? Mishimoto says no one else has had this problem, but says they started using "Dowty seals" in place of O-rings. They're sending me one for me to try.

[rf900rkw]

"You are the only one having problems" followed closely by "We changed the design". Heard it way to often.

I haven't had an official stencilled "X-line" radiator in my hands. But I can tell you the three core radiators coming out of China have a tapered pipe nipple for the drain port. If Mish is screwing a straight tread and o-ring plug into it, that would explain the leak.

[TiminMb]

If I'm going to order an s54 radiator from a local parts supplier, will any year of s54 be a fit?

[QuestMCoupe]

Yes...01 or 02.

[ZoO]

hmm i have one waiting to be installed, anything i can do to prevent or check for leaks before installing?

[rf900rkw]

Joe, I thought your leaks were both VSL radiators? The Chinese/Mish 3-rows haven't been out that long.

[Mishimoto]

2 Mishimoto X-Line radiators and 2 leaky drain plugs. Mishimoto sent new O-rings and then a new radiator because first one dripped like a leaky faucet. Now the second one is dripping after 18 months and 1,500 mi. I've tried to follow Mishimoto's directions to tighten the plug finger tight plus 1/4 turn. But, even finger tight causes the O-ring to squeeze out and leak. So, finger tight plus 1/4 turn seems out of the question. The threads on the plug are very loose (sloppy) and Teflon thread tape doesn't work. What am I doing wrong? Mishimoto says no one else has had this problem, but says they started using "Dowty seals" in place of O-rings. They're sending me one for me to try.

Sorry to hear you are having issues with the drain plug on our Z3 unit. As noted by our customer service team, we have very few claims for this particular radiator. A majority of the issues reported can be attributed to flex of the radiator support which translates to the core. Some of this can be resolved by inspecting/replacing radiator bushings. A leaky drain plug is not something we commonly see. Sounds like we need to take a close look at our existing product to determine if this is a defect spanning our entire batch. We are replacing our O-rings with a dowty seal for the drain plug, which has created a more effective seal. If this does not work for you, please shoot us a PM and we can definitely look into alternate methods to provide a solution for you.

Again, I apologize for the issue you are experiencing.

-John

hmm i have one waiting to be installed, anything i can do to prevent or check for leaks before installing?

As previously noted, very few reports of issues exist. We have a ton of folks using this radiator without concern. Be sure to check out your radiator bushings for wear and replace as necessary. We do recommend the use of Teflon tape on the threads of the drain plug for additional protection against leaks.

If you ever run into any issues, feel free to shoot us a PM.

Thanks
-John

[jajou318]

Rofl radiator bushings? Goes to show that anyone reading this should not buy a mishimoto radiator.

[ZoO]

As previously noted, very few reports of issues exist. We have a ton of folks using this radiator without concern. Be sure to check out your radiator bushings for wear and replace as necessary. We do recommend the use of Teflon tape on the threads of the drain plug for additional protection against leaks.

If you ever run into any issues, feel free to shoot us a PM.

Thanks
-John

i currently have nothing wrong with my current radiator, i just thought a new one would look better under the hood. if the new one leaks, im 100% sure it wont be due to the bushings.

[rf900rkw]

Rofl radiator bushings? Goes to show that anyone reading this should not buy a mishimoto radiator. [

+1. What utter idiocy.


The radiator is mounted in rubber that rests in plastic that is attached to the core support. The plastic headlights are also attached to the core support. You are honestly trying to pass off the radiator failures as core support flex? Yet the headlights aren't shattering?

Teflon tape is ONLY for connections where the threads themselves are the seal. Almost always this will be tapered pipe threads. Any design that uses a different sealing method, gaskets, o-rings, etc, should not have tape used. If you have to use tape to seal up a straight thread with o-ring, there is something else wrong. In this case it is most likely that the Chinese radiators you are reselling have a tapered pipe thread drain nipple.

[BD40]

Randy,
As far as I can tell, the drain port has straight threads and the plug does too. There is enough slop in how the threads mate that there is more than 1/16" side to side play when the plug is 1/4 turn from being seated. (Hope that description makes sense.) I am skeptical about the Dowty seal fix because the face of the drain port is internally chamfered and if I understand Dowty seals, they work best when sealing against a flat face.

"You are the only one having problems" followed closely by "We changed the design". Heard it way to often.

I haven't had an official stencilled "X-line" radiator in my hands. But I can tell you the three core radiators coming out of China have a tapered pipe nipple for the drain port. If Mish is screwing a straight tread and o-ring plug into it, that would explain the leak.

- - - Updated - - -

Holding my breath out here in California.

[QuestMCoupe]

Joe, I thought your leaks were both VSL radiators? The Chinese/Mish 3-rows haven't been out that long.

You're right. Mine we VSL radiaitors.

Carry on...

[kornfeld]

On my previous car I installed a no name aluminum radiator that was pretty fantastic. By all indications, it was the same as those that Mishimoto sold for that model.

On the recommendation of others, I replaced the plug it came with with a 1/4" NPT plug. It threaded much more snugly than what came with the radiator. I only offer this as another data point...might be unrelated to your situation; might help you to do something similar; or who knows, maybe the threaded plug at the bottom is identical and needs a 1/4" NPT plug.

[spacecowboy]

Has anyone used a thread pitch gauge on the port & the plug yet? That would be the easiest way to figure out if there's a thread pitch mismatch.

[BD40]

The radiator shop tried a 1/4" NPT threaded plug. It didn't match. He tried every plug he had and none of them matched. His solution was to drill out and retap the drain port. Not what you'd expect for a $300+ radiator.

On my previous car I installed a no name aluminum radiator that was pretty fantastic. By all indications, it was the same as those that Mishimoto sold for that model.

On the recommendation of others, I replaced the plug it came with with a 1/4" NPT plug. It threaded much more snugly than what came with the radiator. I only offer this as another data point...might be unrelated to your situation; might help you to do something similar; or who knows, maybe the threaded plug at the bottom is identical and needs a 1/4" NPT plug.

[Tim95M3]

Some China-made parts are great, and some are not. Although, I have had a Mishimoto in my E36 for quite some time... actually three E36es and have never had a single problem. Actually had a mechanical fan explode and put a huge dent in my hood, gouge the shit out of the radiator and it STILL held up fine. Guess some are better than others...

[Mishimoto]

Rofl radiator bushings? Goes to show that anyone reading this should not buy a mishimoto radiator.

+1. What utter idiocy.

The radiator is mounted in rubber that rests in plastic that is attached to the core support. The plastic headlights are also attached to the core support. You are honestly trying to pass off the radiator failures as core support flex? Yet the headlights aren't shattering?

Teflon tape is ONLY for connections where the threads themselves are the seal. Almost always this will be tapered pipe threads. Any design that uses a different sealing method, gaskets, o-rings, etc, should not have tape used. If you have to use tape to seal up a straight thread with o-ring, there is something else wrong. In this case it is most likely that the Chinese radiators you are reselling have a tapered pipe thread drain nipple.

The lower radiator bushing comment was in reference to the post regarding core leaks. I believe this post was later deleted by the user because the radiator in question was of a different brand. We've experienced a few radiators that are susceptible to chassis flex issues, the Jeep Wrangler and Ford Powerstroke are two common models that incur issues. This is something we've also seen in the past with our E36 radiator, which our engineering team addressed in the form of product updates. If we see an unusual failure rate attributed to core leaks with this radiator, we could certainly dig deeper to find the root cause. At this time, failure rates are extremely low. Based on the experience of the OP in this thread, it sounds like we need to take a closer look at the drain plug portion of this radiator to determine if any updates can be made to the design or if this particular radiator was simply a defect of manufacturing.

-John

Randy,
As far as I can tell, the drain port has straight threads and the plug does too. There is enough slop in how the threads mate that there is more than 1/16" side to side play when the plug is 1/4 turn from being seated. (Hope that description makes sense.) I am skeptical about the Dowty seal fix because the face of the drain port is internally chamfered and if I understand Dowty seals, they work best when sealing against a flat face.

- - - Updated - - -

Holding my breath out here in California.

The radiator shop tried a 1/4" NPT threaded plug. It didn't match. He tried every plug he had and none of them matched. His solution was to drill out and retap the drain port. Not what you'd expect for a $300+ radiator.

As previously noted, I apologize for the poor experience and issues you experienced with the radiator. This was not the solution that we would prefer. I am sure our customer team would have had no issue sending out a replacement drain plug and/or radiator in the case that the plug fitment was that far off. I understand waiting for replacement parts is sometimes not possible if the vehicle is daily driven or needed for an event with short notice.

Sending you a PM shortly to gather some more information regarding the warranty process.

-John

Has anyone used a thread pitch gauge on the port & the plug yet? That would be the easiest way to figure out if there's a thread pitch mismatch.

The plug and radiator threads both measure M12 X 1.5, which is a very common drain plug size for our aluminum radiator offerings. We've used a variety of seals on drain plugs in the past and we recently updated to a dowty seal which provides a more reliable seal.

Some China-made parts are great, and some are not. Although, I have had a Mishimoto in my E36 for quite some time... actually three E36es and have never had a single problem. Actually had a mechanical fan explode and put a huge dent in my hood, gouge the shit out of the radiator and it STILL held up fine. Guess some are better than others...

Great to hear the radiators have been working out for you Tim!

-John

[BD40]

It's the OP here to report on the leaky drain plug issue. Mishimoto acted quickly to replace the radiator. This time sending one with a Dowty seal instead of an O-ring on the drain plug. Other than the Dowty seal, the new radiator seems identical to the leaky one (including the loose fitting drain plug threads). I had the radiator pressure tested and it didn't leak down. After driving 50+ miles, there is no detectable leak (so far). We may finally have this solved. I just wish Mishimoto had figured this out before I had to go through three of their radiators on the same car.

[jajou318]

Or anyone else. Glad you got your problem resolved

[Mishimoto]

It's the OP here to report on the leaky drain plug issue. Mishimoto acted quickly to replace the radiator. This time sending one with a Dowty seal instead of an O-ring on the drain plug. Other than the Dowty seal, the new radiator seems identical to the leaky one (including the loose fitting drain plug threads). I had the radiator pressure tested and it didn't leak down. After driving 50+ miles, there is no detectable leak (so far). We may finally have this solved. I just wish Mishimoto had figured this out before I had to go through three of their radiators on the same car.

Great to hear this was resolved. Again, I apologize for the inconvenience.

Thanks
-John

[Nighthawk399]

Mishimoto makes garage.

[roninB4]

I'll begin by apologizing for necro thread revival but came across this thread while searching for solutions to fix my current problem. I also bought a Mishimoto radiator two years ago to replace a partially plugged (as best as I can tell) OEM radiator on my e36 (1998 328is) that was experiencing overheat trouble. A new radiator did cure the overheat trouble symptoms (telltale pressure build) from <30 minutes of driving but I was still experiencing coolant loss. The first clue to my present difficulties was on the drain plug itself when I pulled the radiator out of the box. There were at least 6 or more wraps (full revolutions) of Teflon tape on the plug. Most of my reading/experience says 1-1/2 to 2 wraps is all that's needed. Teflon tape (mine anyway..) is about .002-.003 thick and a standard 2A-2B Class thread (production formed outer/internal) only has a couple of .001's mating material clearance per side anyway. This suggested to me that the thread fitment was possibly a little on the sloppy side to be fluid tight under pressure. I unwound all the tape and checked the fit, it didn't inspire confidence but I put 2 wraps on it and used it anyway because I had nothing else at the moment. Besides, it was a brand new component and perhaps it would work better than I thought. I was pretty happy that I could drive the car further than I previously had been able to, one problem seemed solved, but I noticed my coolant levels continued to be on the low side after driving. I continued to re-fill every two days in hopes that it might buy me enough time to get it properly sorted. I pulled the radiator (which seemed to flow just fine) a couple more times trying to effect a repair to the leaking drain plug, even duplicating the factory 6 revolutions despite what the math told me. I even took a thread micrometer (I've been a toolmaker for 25 years) to measure the thread PD (pitch diameter) of the threads to check for undersized drain plug threads. The plug I got from Mishimoto was a bit under size (.007) for a 6g class thread so I replaced it with a store-bought HHCS in hopes this might work. It didn't really offer a good enough seal when driven at highway speeds despite using some Teflon tape. I pulled the radiator again and trued the surface of the sealing area with a very fine file, being careful to avoid getting any fine particles in the radiator. I then faced the underside of the bolt cap (sealing area) in my lathe and made an aluminum crush washer for it. Installation of both was as good as I was going to get for this without resorting to further measures and I hoped for better results. It did seem to hold for a few short distance test drives at calm speeds so I tried stepping up my pace a bit. No joy as I checked coolant level upon return. To eliminate all possibility of deteriorated hose ends/clamps I tossed some die in last night and went for a 45 minute test drive, changing the pace as I drove. Pulling up in the drive I popped the hood and checked with the "blacklight" for leak source. There was spray on the CAI and along the sides of the radiator yet I couldn't pinpoint a single source until I noticed a couple of drops pooling on the ground below. Getting on my knees I could very clearly see that the coolant was still leaking from the drain plug, my efforts to solve this problem didn't work. I can't tell if the internal threads in the radiator are beyond spec's or not, that's entirely possible to do in aluminum when tapping despite having a sharp tap. I will state that, in my experience/opinion, that a straight thread (vs. a tapered thread) requires more consideration to effectively seal. A tapered thread, like a NPT (tapered pipe thread) has a better chance of sealing but requires more care/attention when being created in the factory. Tapping depth is critical as opposed to just running a straight thread tap through the material. I don't know if this was the reason a straight thread was decided on in the design, I wasn't at that meeting, but I suspect so. A straight thread can be used but the seal is obtained by an extra component, like an "O-ring" used in so many other designs of various things with a sealing requirement. I have been fairly happy with the build quality of the radiator itself, it's more than a little disappointing to see the failure come down to something so basic/simple as a leaky drain plug. I am now faced with the prospect of needing to machine a slightly over-size drain plug that either has a built in groove under the cap for the needed "O-ring" or machine a new drain plug with a ball valve attached and just epoxy the damn thing in because I'm tired of f***ing with such a simple (but critical) issue. Either way I'm going to have to spend even more time to effect a solution for a brand new component that failed from a design flaw. I do not relish the notion of cutting a 1.5 thread (if possible on my inch geared lathe) to effect a RELIABLE repair but I see few other options. I'm damn lucky that I didn't get serious damage to the motor when, suddenly, the temp gauge started heading for the red zone. Immediate shut down and road-side two-stepping to get home was far more than "inconvenient" over the last two years including all the premature oil changes after getting home. I left feedback on Amazon about this not long after I noticed the trouble but apparently this did not get very far up the food chain at the factory. I don't know how "isolated" this problem is or how many others have experienced similar trouble but I think there's been enough for other prospective buyers to reconsider the purchase unless the design of said drain has been changed. As for changing to a Dowty Seal, I think that speaks for itself as a bandaid on an expensive, but otherwise nice, product. That's enough b*tching, I've got work to do.

[raubritter]

I have a VSL radiator, but it sounds like a similar situation: straight thread, loose fitting drain plug with o-ring.

Just a thought, but what I tried the last time I did the coolant was get a thinner, smaller diameter buna rubber o-ring that when the drain plug is screwed in, would fit into the chamfer on the radiator, so that the chamfer would act as a groove for the o-ring with the flat drain plug face pressing against it. A bigger, looser-fitting o-ring can sort of ooze out of the chamfer, so I figured a more compact one would stay in the chamfer better. It's working so far.

Other idea: What about using a gasket-maker liquid (like RTV but the one specifically for water pumps) to seal the threads? And/or maybe put some on the drain plug head where the o-ring touches to replace or help the o-ring?

[roninB4]

Buna rubber has an upper limit of 250 degrees Fahrenheit. That's a bit too close to the operating temp of coolant for me to want to rely upon given the variance of product composition. A silicone or Viton seal would be a much better choice (higher heat range) but I can't seem to locate without buying 100 of them. RTV may be a better choice but I'd prefer to avoid something messy like that I'd have to clean up every drain cycle if possible (but thanks for the suggestion). After mucking with this off/on for the last two years I'd just as soon have something simple/reliable that allows for drain capability like it should have had in the first place. Having confidence in a repair pays dividends when night time driving on a road far from home.