Coming off the success of my IP install last weekend, I took advantage of the recent good weather to replace my heater hoses and do a coolant flush.

I also replaced the t-stat.

I thought I had the system vented (on ramps, it bubbled through a few times and added coolant as needed). However, I left the vent screw on the t-stat housing loose and it worked it's way off on the test drive.

I didn't notice any steam at first, but the temp gauge started rising quickly when I went up a hill. It never reached the red, but stayed north of 200. I reckoned that I had a bubble in the coolant and that it would work itself out eventually.

I kept driving and was a few miles from home when I noticed steam coming from under the hood so I pulled over. The aux fan kicked in when I shut off the engine.

There was moisture all over the engine compartment but I couldn't figure out where it was coming from.

I noticed that the radiator cap was cool to the touch, so I open up the radiator. It was empty, so I dumped in some spare coolant brought along for just this contingency.

I started the car and drove a mile back home when it started steaming again. I pulled over into a parking lot and I finally saw that the was steam coming from the t-stat housing where the vent plug should have been.

Fortunately, there was a motorcycle shop nearby and I managed to get a bolt that would work to seal it up until I could get home. I also had to add some more coolant...about a gallon total at this point.

Once home, the radiator was still cool. I also found the original bolt on top of the engine, so it went back in.

Anyway, I figured that I still had a bubble somewhere in the engine...somewhat cool radiator but engine at 200F.

I removed the t-stat housing and noticed it was dry below the t-stat. So, I added a splash of coolant until it poured out. It seems, then, that the block beneath the t-stat was dry and possibly had been so for the entire 7-8 mile trip.

I bolted everything up and topped off the radiator. The second I backed down the driveway (moderately steep), the temp gauge dropped back to 180 where it stayed during the follow up drive.

I had to another splash of coolant once back home, figuring that the system was still filling up.

I took it out again last night. No issues, except that I had to add yet another quart of coolant to the radiator.

I'm starting to get concerned about the need to keep adding coolant. Granted, I lost some coolant with the loose vent plug but I've now had to add about twice as much coolant as the engine needs and in small stages after driving.

I understand these 616s are forgiving engines, but I'm the lord of all klutzes.

Is it the case that it will take some time to get the system fully vented or should I start looking at a leaky head gasket? Any quick and easy checks to make sure it's ok?

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1974 240D "Boldie" 170K.- New timing chain/freshly rebuilt IP/replaced valve seals/injectors/upgraded stereo/new Bilsteins with Yokohamas/fresh paint and rocker panels plus lots of welds.

Well that was an unhappy experience. No doubt it has happened before and will happen again. even experts miss a bolt or screw now and then. But it really pays to do a double check when you think you are finished. Hopefully to didn't do great damage. But you must continue to work on it and find where the coolant is going. Fill it and let it set over night. Check it when next you are going to start it up. If you check it and coolant is down you have a problem with coolant going somewhere and you must find out where. If coolant is up, drive it with your eye on the temp gauge until you know you have the problem behind you. Hope your oil usage doesn't go out of sight.

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Junqueyardjim
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important. C.S. Lewis



1983 Mercedes W123 240D 4 Speed 285,000 on the road with a 617 turbo, beautiful butter yellow, license plate # 83 240D INDIANA

2003 Jaguar Type X, AWD. beautiful, good mileage,
Mom's car, but I won't let her drive it!

Thanks!

I might have dodged a bullet as my after work checks don't hint at anything being abnormal.

Since the weather is iffy and my car freshly painted, I let it idle in the garage for about a 1/2 hour instead of taking it on the road.

I will detail what I checked in case anyone searching later comes across this thread.

Anyway, there was no seepage on the floor overnight and the oil level was the same as when I checked it last week (a topic for another thread).

I removed the radiator cap and kept looking for exhaust bubbles in the coolant. There were no bubbles until the thermostat opened, at which point the entire radiator was gurgling over and splashing out. So I then replaced the cap.

The temperature remained at 180 throughout which is another good sign that there's no exhaust gasses heating the coolant.

There was some greyish exhaust which was really more of a haze. The car has done this since I got it,both before and after the IP rebuild. It smelled normal. I held a paper towel close to the exhaust for about a minute and the towel was still dry.

I keep checking the radiator as it cools off and so far it's mantaining the same level as before I stated it. Still no leaks on the garage floor or wetness on the block.

I'm not out of the woods yet as perhaps an hour or two of driving could yield a lower radiator level, but at least I can sleep a little better tonight.


If and when the weather clears up and the salt washes off the road, I'll take it out and report back should anything happen.

Tighten that vent screw, gents!

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1974 240D "Boldie" 170K.- New timing chain/freshly rebuilt IP/replaced valve seals/injectors/upgraded stereo/new Bilsteins with Yokohamas/fresh paint and rocker panels plus lots of welds.