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Hey all. I've been struggling to figure out the cause of my chronic coolant leak on my '89 2.6 for the past couple weeks to no avail. Upon reaching idle temp (I assume its at this point) most coolant spews out of the coolant overflow line just below the reservoir cap. At which point the coolant likes to level out just a tad underneath the coolant level sensor and does not dip past that level. So far I've replaced the thermostat, reservoir cap, and a LOT of coolant. I'd appreciate any help I can get, as I'm about at my wits end with this machine. Thanks.
I should note that this all occurred after I replaced my head gasket. Not sure if there is any correlation, but the coolant system was dry for about a couple days to a week.
As far as I can tell the only spot coolant exits the system is out of the coolant overflow line just below the coolant expansion tank cap. Part of me thinks theres way too much pressure inside of the tank, pushing that spring up and allowing coolant to spew out. I have no idea how, though. I dont see any coolant in my engine bay in any place other than that overflow line.
As far as I can tell the only spot coolant exits the system is out of the coolant overflow line just below the coolant expansion tank cap. Part of me thinks theres way too much pressure inside of the tank, pushing that spring up and allowing coolant to spew out. I have no idea how, though. I dont see any coolant in my engine bay in any place other than that overflow line.
Excess pressure in the cooling system can be caused by partial blockage, internally, or externally.
Kinked or twisted hoses can be the cause of external blockages.
Any inefficiency in the cooling system can cause hot spots. Any hotspot that allows the formation of steam, can cause exponential increases in pressure.
Steam expands at about 1600 to 1 in volume, and, in a closed system just a degree or 2 rise in temperature can cause doubling of pressure when the coolant (water) becomes superheated.
Sounds to me like you should take it back to whomever did you headgasket. could be something as silly as its been put on upside down. have you tried pressure test (positive press from rad cap physically exposing the leak) or combustion leak test (color change dye when gases are exposed to coolant)?
not sure if vatozone or autoparts could rent you, but they could be had inexpensive online or through retails like hazardousfreight. might be worthwhile to purchase along with fuel press tester if planning on keeping/driving older cars.
I went ahead and ordered some radiator hoses as per MB2timer's advice (also they had slight bubbling near the ports so figured it would be worth it), so hopefully that could alleviate the issue. And to address theonlyone, I did my own head gasket. I made sure it was done correctly and double checked every step. I used a Vreinz gasket, and they cant be put on upside down due to the orientation of the top of the block. You aren't the first to tell me to leak down test so that will be my next step. Thank you both for your help and I'll let you know if either gives me any info!
thanks for the reply isntgay! im rooting you on your awesome for even trying on your own!!!
I also wonder if something could have been dislodged in passageway like rust particles or rtv. i hope its resolved soon. like to see more of these cars stay on the road and enjoyed.
leak down test= checking to see if valves hold combustion pressure for the most part. low could be valve guides or stemseals.
Last edited by theonlyone; Sep 30, 2025 at 10:54 PM.
thanks for the reply isntgay! im rooting you on your awesome for even trying on your own!!!
I also wonder if something could have been dislodged in passageway like rust particles or rtv. i hope its resolved soon. like to see more of these cars stay on the road and enjoyed.
leak down test= checking to see if valves hold combustion pressure for the most part. low could be valve guides or stemseals.
sorry misread or dyslexia kicked in. thank you for taking it kindly. sucks getting old...
ill probably be banned or have my participation badge taken away, no biggie.
another thing i thought to check was white crusty residue or fresh sweating around inlet/outlet pipes where hoses connect as its plastic on rad and some thermo housing caps were plastic. heater core connections at firewall and heater core (usually damp carpets is a sign). if automatic check atleast the dipstick incase of coolant contamination from failed internal cooler inside rad tank.
Last edited by theonlyone; Oct 1, 2025 at 01:26 AM.
190E 2.6L 1989, 190E 2.6L 1988, BMW 535dXdrive 2014, BMW 428i 2015
I think this was mentioned before but I hope you have tested the radiator cap to see if it is in spec. It is something like 15psi is when it opens to let excess pressure out.
If it is much lower one could experience coolant loss. Happened to me in by W124 when I had it.
I wanted to update you guys, it sadly has not been fixed yet. I've replaced the 2 right side radiator hoses (radiator to thermostat and radiator to water pump). While doing this I did notice some white residue around the ports to the water pump, and possibly the thermostat IIRC. On top of that, I did get a full coolant flush at my local Valvoline. Still no fix.
The strange thing is, once I replaced the hoses and got the flush I tried to recreate the conditions at which it would spew out. I ran the engine at higher RPM's (3k-4k) while stationary. I went through a couple thermostat opening and closing cycles, all with no noticeable coolant loss. It's only when I was driving back from work tonight (slightly spirited driving) at which the coolant light came on. I am completely stumped.
I wanted to update you guys, it sadly has not been fixed yet. I've replaced the 2 right side radiator hoses (radiator to thermostat and radiator to water pump). While doing this I did notice some white residue around the ports to the water pump, and possibly the thermostat IIRC. On top of that, I did get a full coolant flush at my local Valvoline. Still no fix.
The strange thing is, once I replaced the hoses and got the flush I tried to recreate the conditions at which it would spew out. I ran the engine at higher RPM's (3k-4k) while stationary. I went through a couple thermostat opening and closing cycles, all with no noticeable coolant loss. It's only when I was driving back from work tonight (slightly spirited driving) at which the coolant light came on. I am completely stumped.
Was the coolant level low?
Or was it a false indication of low?
This might be a good time to scan for codes.
Also.
After running it, put some cardboard under your car while it’s in your garage, or carport, or driveway.
That may help you identify the source of the leak, the wet spots underneath the dripping.
The leak may boil off some coolant, if it’s hot enough, but when it cools down you should be able to get some drips out of it, then follow them back to the source.
It was low. I topped off the coolant a tad bit higher than I usually do (about a centimeter below the overflow line to the thermostat) and within 30 minutes of driving, the coolant light came on. Upon inspection, the level of coolant was resting slightly below the coolant level sensor.
From what I can see, its originating from the intake side of the engine bay. It's leaking all the way down to the bottom of my engine supports and inner sway bars. There was a very slight pool underneath the port that the heater hose connects to, the one on the head very close to the firewall on the intake side. I tightened that hose clamp and the coolant light still came on. The highest point aside from that is on what I believe to be the starter (see first pic, its in the middle of the photo slightly to the left). I have also attached a general picture of the bottom of my engine bay to see if anyone can gleam anything from that. Its difficult to tell as it seems it only seems to start leaking when I'm driving, typically the coolant light comes on after about 15-20 minutes of driving. If I'm lucky.
as far back is the wetness is its a high chance its heater core related. it was stated a hose on the intake side of the heater core related was tightened and possibly still leaks its obviously time to change the hose. my logic would dictate that if the easiest hoses weren't changed theres a good chance its time to change out all the cooling system hoses at minimum of piece of mind. possibly also coolant level sender, waterpump, and clutchfan just to not stress out over overheating in traffic.
i still recommend pressure testing before hand as it will physically expose leaks (do not over pressurize keep it normal operating psi). depending on the kit you buy/use it may come with adapters to fit your cap for the expansion tank to verify operation as dulcasi has said.
i highly recommend you check out mercedessource on his site or youtube as the guy has explanations more geared toward diy enthusiasts. it also helps to look online at parts diagrams to get a clue as what the repair could entail or what it even should look like on your car. always best to physically remove parts prior to purchase to compare with what the parts place can get. if you want to do it right also look for a physical factory service manual, free pdf, or get subscription to specific car repair info from places like identifix, mitchell1, alldata, etc. if your just a guy whos mildly curious and wants to pay shops to fix all these could partially even be beneficial as to know what expect from the job. (but please don't be that guy who asks for torque wrench calibration certs or has crazy expectations)
Last edited by theonlyone; Oct 5, 2025 at 07:16 PM.
I wanted to update you guys, it sadly has not been fixed yet. I've replaced the 2 right side radiator hoses (radiator to thermostat and radiator to water pump). While doing this I did notice some white residue around the ports to the water pump, and possibly the thermostat IIRC. On top of that, I did get a full coolant flush at my local Valvoline. Still no fix.
The strange thing is, once I replaced the hoses and got the flush I tried to recreate the conditions at which it would spew out. I ran the engine at higher RPM's (3k-4k) while stationary. I went through a couple thermostat opening and closing cycles, all with no noticeable coolant loss. It's only when I was driving back from work tonight (slightly spirited driving) at which the coolant light came on. I am completely stumped.
I guess I'm not understanding why you continue to be reluctant to run some dye in your cooling system to really determine where the leak is. Liquids can travel a long way which means where you guess that the leak might be and where the leak actually is can be 2 very different things. All you're currently doing is guessing where the leak is and then throwing parts at your guess and that continues to not solve the problem. Guessing and throwing parts at a problem without solving the problem can get very expensive, very fast.
I guess I'm not understanding why you continue to be reluctant to run some dye in your cooling system to really determine where the leak is. Liquids can travel a long way which means where you guess that the leak might be and where the leak actually is can be 2 very different things. All you're currently doing is guessing where the leak is and then throwing parts at your guess and that continues to not solve the problem. Guessing and throwing parts at a problem without solving the problem can get very expensive, very fast.
not sure what kind of dye you are referring to; i am guessing uv like for aircon. but that is not always thorough enough as it will not tell you pressure drops (verifying repair). you are at the mercy of visibility which can tend to be poor and awkward even using lights, mirrors, and endoscopes. the radiator pressure test simulates operating condition at pressure (yes no circulation or heat as the engine is not running) but can expose pinhole sprays or drips which can be easier to locate or atleast have a clue where to look on demand. in your case if its leaking that bad its probably still wet or if dry creates white powder or rust stains to guide you to the problem.
you can always print parts diagram of things like intake assembly, cooling system, or heater to visually digest and compare with what you see physically to know where to put your hand to check for coolant leaks or the removal of components to get better access.
i get that everybody hates parts changers, but you walk a fine line sometimes especially with old cars as the next weakest component link could fail or the new part has defects and stir the frustration all over again. its just the nature of car ownership in my eyes; probably why so many people these days just lease vehicles.
not sure what kind of dye you are referring to; i am guessing uv like for aircon. but that is not always thorough enough as it will not tell you pressure drops (verifying repair). you are at the mercy of visibility which can tend to be poor and awkward even using lights, mirrors, and endoscopes. the radiator pressure test simulates operating condition at pressure (yes no circulation or heat as the engine is not running) but can expose pinhole sprays or drips which can be easier to locate or atleast have a clue where to look on demand. in your case if its leaking that bad its probably still wet or if dry creates white powder or rust stains to guide you to the problem.
you can always print parts diagram of things like intake assembly, cooling system, or heater to visually digest and compare with what you see physically to know where to put your hand to check for coolant leaks or the removal of components to get better access.
i get that everybody hates parts changers, but you walk a fine line sometimes especially with old cars as the next weakest component link could fail or the new part has defects and stir the frustration all over again. its just the nature of car ownership in my eyes; probably why so many people these days just lease vehicles.
Pay a visit to your local parts store. They can help you. Dyes are good for helping to determine where a leak is originating from. Liquids can travel long distances which is why where an area has dried liquid on it is not always where the leak originated from. You keep buying parts and you still have the leak so that your guesses as to where the leak is aren't solving the problem..
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