Leaking thermostat
01-19-2019, 10:41 PM
#1
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Thread Starter
Leaking thermostat
Hello everyone, I am at my wits end. I have a 2009 GL550 with 95k miles. Last Tuesday code P0128 came up, I changed the thermostat with a Mahle brand. For whatever reason the coolant kept leaking. As soon as I poured in coolant, I actually heard it leak out, I had a catch bucket under the car and literally heard and saw the coolant leaking out. I removed and reinstalled this particular thermostat (3) three times that night, same result each time. I finally returned that thermostat and purchased one from the dealer. Installed that one and ran the truck for approximately and hour, no leak. Woke up in the morning and saw coolant on the ground
. This thermostat is leaking also. I tightened the bolts equally, couldn't find the torque specs but, it's tight. I'm racking my brain here at the moment and to make matters worse, the red battery light came on tonight. I'll deal with that later. My main concern is this coolant leak. Has anyone ever experienced anything like this before? Any help, or suggestions will be greatly appreciated.
Rich
. This thermostat is leaking also. I tightened the bolts equally, couldn't find the torque specs but, it's tight. I'm racking my brain here at the moment and to make matters worse, the red battery light came on tonight. I'll deal with that later. My main concern is this coolant leak. Has anyone ever experienced anything like this before? Any help, or suggestions will be greatly appreciated. Rich
01-20-2019, 10:22 AM
#2
MBWorld Fanatic!
I can't see how the actual thermostat would cause (or fix) a leak. The thermostat housing, however, yes - that would. Assume that is what you are referring to? This shouldn't be too hard to figure out if you look over things closely. The two mating surfaces and the gasket. You didn't mention anything about the gasket?
Where exactly is the fluid leaking from?
What is that code?
Why did you change the assembly in the first place? Was it just because of that code or was it also leaking? Look at the mating surfaces for corrosion. If it's leaking as bad as you say it is, something is very obviously wrong - which also means it's very obvious to spot why it's wrong.
Did you get all the old gasket off... ALL of it? A little less likely, but it's possible you overtightened and deformed the housing.
Where exactly is the fluid leaking from?
What is that code?
Why did you change the assembly in the first place? Was it just because of that code or was it also leaking? Look at the mating surfaces for corrosion. If it's leaking as bad as you say it is, something is very obviously wrong - which also means it's very obvious to spot why it's wrong.
Did you get all the old gasket off... ALL of it? A little less likely, but it's possible you overtightened and deformed the housing.
Last edited by DennisG01; 01-20-2019 at 11:36 AM.
01-20-2019, 03:20 PM
#3
Member
Thread Starter
I can't see how the actual thermostat would cause (or fix) a leak. The thermostat housing, however, yes - that would. Assume that is what you are referring to? This shouldn't be too hard to figure out if you look over things closely. The two mating surfaces and the gasket. You didn't mention anything about the gasket?
Where exactly is the fluid leaking from?
What is that code?
Why did you change the assembly in the first place? Was it just because of that code or was it also leaking? Look at the mating surfaces for corrosion. If it's leaking as bad as you say it is, something is very obviously wrong - which also means it's very obvious to spot why it's wrong.
Did you get all the old gasket off... ALL of it? A little less likely, but it's possible you overtightened and deformed the housing.
Where exactly is the fluid leaking from?
What is that code?
Why did you change the assembly in the first place? Was it just because of that code or was it also leaking? Look at the mating surfaces for corrosion. If it's leaking as bad as you say it is, something is very obviously wrong - which also means it's very obvious to spot why it's wrong.
Did you get all the old gasket off... ALL of it? A little less likely, but it's possible you overtightened and deformed the housing.
01-20-2019, 09:45 PM
#4
MBWorld Fanatic!
I can't see how the actual thermostat would cause (or fix) a leak. The thermostat housing, however, yes - that would. Assume that is what you are referring to? This shouldn't be too hard to figure out if you look over things closely. The two mating surfaces and the gasket. You didn't mention anything about the gasket?
Where exactly is the fluid leaking from?
What is that code?
Why did you change the assembly in the first place? Was it just because of that code or was it also leaking? Look at the mating surfaces for corrosion. If it's leaking as bad as you say it is, something is very obviously wrong - which also means it's very obvious to spot why it's wrong.
Did you get all the old gasket off... ALL of it? A little less likely, but it's possible you overtightened and deformed the housing.
Where exactly is the fluid leaking from?
What is that code?
Why did you change the assembly in the first place? Was it just because of that code or was it also leaking? Look at the mating surfaces for corrosion. If it's leaking as bad as you say it is, something is very obviously wrong - which also means it's very obvious to spot why it's wrong.
Did you get all the old gasket off... ALL of it? A little less likely, but it's possible you overtightened and deformed the housing.
Red light... that could mean that your alternator isn't putting out the proper voltage. Check that ASAP. Either through the dash display or at the jump post under the hood or, ideally, directly at battery. Otherwise you could end up stranded somewhere.
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rich30769 (01-21-2019)
01-21-2019, 06:20 AM
#5
Member
Thread Starter
So nothing was leaking before you did the swap? Look for gasket pieces still stuck and/or where you missed putting the new one on.
Red light... that could mean that your alternator isn't putting out the proper voltage. Check that ASAP. Either through the dash display or at the jump post under the hood or, ideally, directly at battery. Otherwise you could end up stranded somewhere.
Red light... that could mean that your alternator isn't putting out the proper voltage. Check that ASAP. Either through the dash display or at the jump post under the hood or, ideally, directly at battery. Otherwise you could end up stranded somewhere.
Thanks DennisG01
01-21-2019, 10:39 AM
#6
MBWorld Fanatic!
Depending on where you checked the voltage from the alternator, it could also be loose or dirty connections somewhere along the line. Since you ID'd low V as the symptom, no figure out the cause. How easy is it to get directly to your alternator and check there?
Good luck! I'm betting that the t-stat issue/fix will be a simple one.
Good luck! I'm betting that the t-stat issue/fix will be a simple one.
01-23-2019, 01:37 PM
#7
Definitely no leak before the swap, have to find out what has caused this. Hopefully it is something as simple as gasket remnants. As for the red light, alternator wasn't putting out the proper voltage so, that will be changed asap. Too cold at the moment to work on anything so, once it warms up i'll take apart and reassemble.
Thanks DennisG01
Thanks DennisG01
1. Make sure you install the gasket properly
2. Make sure you did not damage the surface when removing the old T-stat. If you have a deep scratch or something like that, gasket wont fix it. Make sure you clean the surface to remove the old gasket.
3. Are you sure it's tight when you reattach? Maybe the bolts striped and do not tighten properly? Be careful not to over tighten.
4. Are you sure it's leaking from T-stat and not from somewhere else like water pump, hose and such?
Good luck
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01-23-2019, 05:33 PM
#8
Member
Thread Starter
There should be something visibly wrong for a leak like that.
1. Make sure you install the gasket properly
2. Make sure you did not damage the surface when removing the old T-stat. If you have a deep scratch or something like that, gasket wont fix it. Make sure you clean the surface to remove the old gasket.
3. Are you sure it's tight when you reattach? Maybe the bolts striped and do not tighten properly? Be careful not to over tighten.
4. Are you sure it's leaking from T-stat and not from somewhere else like water pump, hose and such?
Good luck
1. Make sure you install the gasket properly
2. Make sure you did not damage the surface when removing the old T-stat. If you have a deep scratch or something like that, gasket wont fix it. Make sure you clean the surface to remove the old gasket.
3. Are you sure it's tight when you reattach? Maybe the bolts striped and do not tighten properly? Be careful not to over tighten.
4. Are you sure it's leaking from T-stat and not from somewhere else like water pump, hose and such?
Good luck
Does anyone know the torque specs? 10Nm?
01-24-2019, 09:51 AM
#9
At least for my truck it was definitely more than 10Nm. I do not have a manual in front of me so I cannot say for sure
01-24-2019, 04:41 PM
#10
Thermostat housing to timing cover bolts - 25 Nm
01-24-2019, 08:19 PM
#11
Member
Thread Starter
Thank you... Ok an update. Took thermostat housing off, cleaned off what looked like it may possibly cause an issue, reinstalled, hand tightened top and bottom bolts, then tighten both bolts snug with ratchett. As soon as I started to pour in coolant I heard something, went over to have a look and sure enough, leaking from the top of the housing 
Tightened bolts some more because now I'm getting pissed, and still leaking. It seems as if there's a very miniscule gap between the housing, gasket and block. Something has to be warped, there's no cracks, or anything that I can see with the naked eye so, I'm leaning towards the warped angle. How this happened, I have no idea. What should have been a 30/45 min job has turned into a nightmare, lol. Next step, have towed to shop to see what they find 
Tightened bolts some more because now I'm getting pissed, and still leaking. It seems as if there's a very miniscule gap between the housing, gasket and block. Something has to be warped, there's no cracks, or anything that I can see with the naked eye so, I'm leaning towards the warped angle. How this happened, I have no idea. What should have been a 30/45 min job has turned into a nightmare, lol. Next step, have towed to shop to see what they find
01-25-2019, 08:31 AM
#12
MBWorld Fanatic!
Well that certainly stinks. If you have a good straight edge, you could check the mating surface (engine side) for true.
Have you thought about just making your own gasket with RTV? Not just a "smear", but a small bead that you first let partially cure. Then attach the t-stat housing and tighten only a little bit till you contact the bead and feel it squish a tiny amount. Let it fully cure, then tighten the rest of the way. That should take up any imperfections in the surface. Depending on how bad the surface is, you may get away with a nice smear on both sides of the gasket, as well.
Have you thought about just making your own gasket with RTV? Not just a "smear", but a small bead that you first let partially cure. Then attach the t-stat housing and tighten only a little bit till you contact the bead and feel it squish a tiny amount. Let it fully cure, then tighten the rest of the way. That should take up any imperfections in the surface. Depending on how bad the surface is, you may get away with a nice smear on both sides of the gasket, as well.
01-25-2019, 09:08 AM
#13
Member
Thread Starter
Well that certainly stinks. If you have a good straight edge, you could check the mating surface (engine side) for true.
Have you thought about just making your own gasket with RTV? Not just a "smear", but a small bead that you first let partially cure. Then attach the t-stat housing and tighten only a little bit till you contact the bead and feel it squish a tiny amount. Let it fully cure, then tighten the rest of the way. That should take up any imperfections in the surface. Depending on how bad the surface is, you may get away with a nice smear on both sides of the gasket, as well.
Have you thought about just making your own gasket with RTV? Not just a "smear", but a small bead that you first let partially cure. Then attach the t-stat housing and tighten only a little bit till you contact the bead and feel it squish a tiny amount. Let it fully cure, then tighten the rest of the way. That should take up any imperfections in the surface. Depending on how bad the surface is, you may get away with a nice smear on both sides of the gasket, as well.
I am seriously considering doing that. I just have to wait until next week due to prior commitments. Something so simple turns into this. Thanks for your help and suggestions.
01-25-2019, 10:35 AM
#14
Assuming the gap is small, you can also try cutting your own gasket from an appropriate material. I see these universal gasket kits at my auto store once in a while. I would do that combined with a thin layer of RTV on both side.
Do you still have your old thermostat? Is the surface area warped a bit?
Do you still have your old thermostat? Is the surface area warped a bit?
01-25-2019, 12:17 PM
#15
Member
Thread Starter
Assuming the gap is small, you can also try cutting your own gasket from an appropriate material. I see these universal gasket kits at my auto store once in a while. I would do that combined with a thin layer of RTV on both side.
Do you still have your old thermostat? Is the surface area warped a bit?
Do you still have your old thermostat? Is the surface area warped a bit?
01-26-2019, 04:24 PM
#16
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Have you thought about just making your own gasket with RTV? Not just a "smear", but a small bead that you first let partially cure. Then attach the t-stat housing and tighten only a little bit till you contact the bead and feel it squish a tiny amount. Let it fully cure, then tighten the rest of the way. That should take up any imperfections in the surface. Depending on how bad the surface is, you may get away with a nice smear on both sides of the gasket, as well.
Put down a bead of silicone, torque the bolts till they're snug (the silicone is bulging out), wait 24 hrs, then give the bolts another 1/8 turn. This puts the cured rubber under compression and thus it acts like a washer, helping prevent the bolt from backing out.
Most people like to use specialty automotive silicone, especially when in contact with oil, but I drove ~300 miles on regular silicone caulk holding back oil on my cam housing plugs.
01-26-2019, 11:36 PM
#17
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Thread Starter
We used to do gaskets like that all the time on racing motors. It's better than a paper gasket. The reason people don't do it everywhere is because you have to let it set undisturbed for a few hours and the prep work is more involved.
Put down a bead of silicone, torque the bolts till they're snug (the silicone is bulging out), wait 24 hrs, then give the bolts another 1/8 turn. This puts the cured rubber under compression and thus it acts like a washer, helping prevent the bolt from backing out.
Most people like to use specialty automotive silicone, especially when in contact with oil, but I drove ~300 miles on regular silicone caulk holding back oil on my cam housing plugs.
Put down a bead of silicone, torque the bolts till they're snug (the silicone is bulging out), wait 24 hrs, then give the bolts another 1/8 turn. This puts the cured rubber under compression and thus it acts like a washer, helping prevent the bolt from backing out.
Most people like to use specialty automotive silicone, especially when in contact with oil, but I drove ~300 miles on regular silicone caulk holding back oil on my cam housing plugs.
01-27-2019, 10:54 AM
#18
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2007 GL450
Tomorrow may be the last nice day here for a week, or two so, I'm going to use the silicone the way a few have suggested. I really need this to work because, I can't keep driving this Lexus because it's lowered etc., and it's not a winter car at all and the truck is 100% my daily driver.
01-27-2019, 07:09 PM
#19
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Thread Starter
Just finished putting the thermostat back in with a bead of Grey Permatex RTV silicone specifically for "themostat housing and water pump." Did the finger tightening, then took on the job of removing alternator, heavy as hell, btw. Went back and snugged the bolts up on the thermostat, then completed the install of alternator. Did I mention heavy as hell? Now I'll wait till I get home from work tomorrow to add the coolant. Hopefully all is well after tonight.
01-27-2019, 08:04 PM
#20
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Rich, Sure hope your latest silicone application works. We all know having this type of leak, especially not knowing for sure the fix is very frustrating.
Eric, Very much appreciate your calm advice and sure hope it works with no leaks for Rich!
James
Eric, Very much appreciate your calm advice and sure hope it works with no leaks for Rich!
James
01-27-2019, 08:31 PM
#21
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Just finished putting the thermostat back in with a bead of Grey Permatex RTV silicone specifically for "themostat housing and water pump." Did the finger tightening, then took on the job of removing alternator, heavy as hell, btw. Went back and snugged the bolts up on the thermostat, then completed the install of alternator. Did I mention heavy as hell? Now I'll wait till I get home from work tomorrow to add the coolant. Hopefully all is well after tonight.
My pleasure, of course.
Last edited by eric_in_sd; 01-27-2019 at 08:33 PM.
01-27-2019, 09:28 PM
#22
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[QUOTE=eric_in_sd;7665819]Sounds good. Curious - did you let it cure before tightening? Technically that's the superior method, though we'd often just snug the bolts with the silicone wet. Post back whether all is well.
Honestly, only for about 1 1/2hr to 2hrs with just finger tightness, then snugged tightened with ratchet. I'll pour the coolant in around 430/5 tomorrow evening
Honestly, only for about 1 1/2hr to 2hrs with just finger tightness, then snugged tightened with ratchet. I'll pour the coolant in around 430/5 tomorrow evening
01-27-2019, 09:30 PM
#23
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[QUOTE=JamesMitchell;7665801]Rich, Sure hope your latest silicone application works. We all know having this type of leak, especially not knowing for sure the fix is very frustrating.
Thanks JamesMitchell,
Frustrating is an understatement at this point, especially when I know that type of job normally takes me 30 to 40 mins to do.
Thanks JamesMitchell,
Frustrating is an understatement at this point, especially when I know that type of job normally takes me 30 to 40 mins to do.
01-28-2019, 06:05 PM
#24
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I want to thank all of you for hanging in there with me, the silicone was a success. The truck has been running for and hour with no leaks in site. You truly have to love this forum community, I truly appreciate all of you and your help and suggestions.
