Did I Damage My Head Gasket--1998 E300 - PeachParts Mercedes-Benz Forum

RLGDiesel · #1 05-19-2014, 12:17 PM

So I need some reassurance that I didn't turn a minor repair into a bigger one this weekend...

Story: I changed the thermostat on my 1998 E300 a couple days ago and lost a lot of coolant in the process. I refilled the expansion tank with about 1 gallon and restarted the car with the cap off. I planned to let it run for a few minutes to let any air in the system out. When I walked to the front of the car, however, I noticed coolant overflowing out of the top of the tank. I capped the reservoir instinctively because it was making a mess on the garage floor. I let the car idle for several minutes until it reached 78-80*C since I was mainly concerned about leaks. At that time the heater was still cold and neither the upper and lower radiator hoses were hot either.

I realized I still had air in the cooling system, so I let the car cool down overnight. I woke up the next morning and started the car with the cap off. The coolant stayed at full until I revved the engine and held it at 2000 for 2-4 minutes at a time. I refilled the reservoir repeatedly during this process until I added another gallon to the system. The temperature never got above 90-95 during this process (higher than normal but not dangerous per gauge).

What I'm worried about are the ~10 minute periods that I ran the car with air bubbles in the system. Since the expansion tank stayed full before I revved it and I later added another gallon, could the aluminum head have been running with only 2 quarts of coolant and mainly air for a brief period. As I read about proper bleeding procedures, I also heard about head gasket damage caused by "hotspots," "air pockets," and "cavitation." I didn't want to save a few bucks doing this myself and end up damaging something because I don't have the same vacuum fill technique as the dealer.

Thanks!

Luke

Chris W. · #2 05-19-2014, 12:57 PM

My opinion? Nothing to worry about.

Rgds,
Chris W.
'95 E300D, 419K

Zulfiqar · #3 05-19-2014, 01:00 PM

as long as the engine never overheated - you are most likely safe. For refilling these engines I follow whunter's advice.

slowly fill the engine from the top hose - it will take about a gallon, when it starts to back up, attach the hose to the radiator, now fill from the tank - slowly. It will take nearly all of the remaining gallon, leave cap off and start engine - wait till the gauge registers approximately 80C. the thermostat valve will open and air will be pushed out from the bleed port in the radiator. Close off cap and let it idle.

Diesel911 · #4 05-19-2014, 01:32 PM

I say you won't know till you drive it some.

No point in removing the Head unless you know there is a problem.

RLGDiesel · #5 05-19-2014, 04:20 PM

Thanks for the replies...I didn't try to upper hose technique because I could only fill it up "about a cup" on the last vehicle I used it on. Good to know that's the way to fill up the 606.

I'm not planning to pull the head...just looking for some peace of mind. I think everything's good.

How important is coolant anyway before the thermostat opens?

Also, wouldn't the gauge register high even if it was just air...I never got above 90-95.

Thanks again!

Luke

uberwasser · #6 05-19-2014, 04:32 PM

To answer your two questions objectively:

The thermostat wouldn't open for a long while without coolant to conduct heat from the engine in to it. Air is a poor conductor compared to water and doesn't flow around inside the engine like the water would, so the thermostat would stay cool longer. In the meantime the engine would be getting hotter than designed in certain areas, likely.

The gauge is only so helpful for issues like this, as it only measures heat in one small area around the sensor probe. It's much more accurate when the engine is full of water/coolant since the water helps distribute heat more evenly through the engine and it's contacing the probe directly. If you have poor flow of coolant, or no coolant, in the engine then heat will build up in places it shouldn't since the cooling system isn't working as designed. This won't be read properly by the temp sensor, and therefore the gauge, since that hot spot may be on the opposite side of the engine. Additionally, if you have air pockets in the cooling system it's possible for an air pocket to be sitting right around the sensor. As mentioned air is a poor heat conductor and so the sensor wouldn't get a good reading of the engine's working temp when surrounded by air.

That all said, you're probably worrying to an excess. We've all been in those shoes!

Drive it and watch it. Odds are good you'll be fine.

jt20 · #7 05-19-2014, 04:41 PM

I agree, not much worth fretting about.

coolant is very important before the thermostat opens, in fact, the t-stat will not even open until long after operating temp is reached in the metal that contacts combustion

Water / liquid absorbs heat and distributes it more evenly. Convection through a liquid is much faster than through air - this solves the problem of localized heating in heads and cylinder walls.

The gauge will top out with just air in the head (near the sensor), but the response is slower and is not truly indicative of head temperature.

nelbur · #8 05-19-2014, 05:05 PM

Your engine has an air bleed bolt on the head just behind the connection for the upper radiator hose, at least my '97 does. It is a fairly large hex head a couple of inches back from the hose. When I fill up with coolant I remove the bolt. Then I screw it in a bit and start the engine and watch the bubbling around the threads. When the bubbles stop I tighten the bolt. I would assume the head is fine until proven otherwise. I doubt there would be a problem since there was some water and the engine was not under load.

RLGDiesel · #9 05-19-2014, 05:22 PM

Very good information so far...especially from what I thought might be construed as a dumb question haha. I definitely learned a lot about my cooling system at least and I guess that's a big part of DIY. Thanks for all y'all's help !

Now one last question: why did the overflow tank stay full until I revved the engine? Shouldn't that gallon of coolant have traveled into the head by gravity via the smaller diameter hose at the bottom of the tank? I thought the system was self bleeding to a certain extent since there was even a jiggle valve on the new t-stat.

86-300sdl · #10 05-19-2014, 07:21 PM

Let the motor (head) cool off before you pour cold water / coolant in through the upper radiator hose.

benedict · #11 05-19-2014, 08:40 PM

Quote:

Originally Posted by RLGDiesel

Very good information so far...especially from what I thought might be construed as a dumb question haha. I definitely learned a lot about my cooling system at least and I guess that's a big part of DIY. Thanks for all y'all's help !

Now one last question: why did the overflow tank stay full until I revved the engine? Shouldn't that gallon of coolant have traveled into the head by gravity via the smaller diameter hose at the bottom of the tank? I thought the system was self bleeding to a certain extent since there was even a jiggle valve on the new t-stat.

You're asking that coolant to push the air away but it doesn't happen just from gravity. Turn a cup upside down and push it down into the water of a swimming pool and see what happens.
They do need to be burped. Best method I've found with mine is as whunter says to remove upper hose from head and pour in your fresh coolant to the brim and put it back together then fill up the expansion tank.

Here is what i also do. I drive around the block a few times with the radiator cap twisted to its first stage off, meaning not all the way off but twisted so there is no more seal. I have a steep hill around the corner and park it with the nose facing upwards (ramps will do the same) for a minute or two, you can see it burping if you pop the hood.

At this stage you probably don't have any heat in the cabin so you'll need to burp that too. This is easier just turn the heat to full on and then rev engine up to 2500rpm briefly 3 times. It usually comes through on the third revup.

A few hot and cold cycles and your coolant level may drop as they continue to bleed-don't panic just top the expansion tank off again.

engatwork · #12 05-19-2014, 08:46 PM

You did not hurt anything.

jay_bob · #13 05-19-2014, 09:21 PM

I concur with the filling method:
- don't forget to close the petcock and the block drain (BTDT)
- most engines and most climates call for 1 gal of G05 and 1 gal of distilled water mixed 50/50.
- elevate the front (ramps or a sloping driveway works)
- remove the upper radiator hose from the radiator neck. Be careful, if the hose is stuck on don't yank on it, you can crack the plastic radiator tank.
- set heater controls on full heat (click the wheel into the max position). You can pull the plug on the mono/duo valve to force it open if your system is not operating properly. If you have a 240D or a manual system set the dials for max heat to open the water valves.
- Pour coolant mix into the disconnected end of the upper radiator hose until it holds no more. A funnel is helpful. Just be sure it's a clean funnel, not one you just used to fill the oil.
- Reconnect hose and pour rest of mix slowly into expansion tank until it is full.
- Leave the pressure cap off.
- Start engine and let it get up to temperature so thermostat opens. Watch the temperature gauge and monitor the heater, you should not go over 90C and you should be getting massive heat out the vents. No need to speed race the engine, just some gentle excursions to 1500-2000/min to get things warmed up and flowing.
- Top off reservoir as necessary. As mentioned above, do not introduce room temperature coolant mix directly into a head at operating temperature. Alway go through the expansion tank.
- Put jug with remainder of mix in trunk. So you'll have it handy as you are out and about.
- Keep an eye on the coolant level and watch the temperature gauge more closely than normal for the next couple days as the remaining trapped air escapes.