Probably just a minor leak someplace. Check all the hose clamps again, when mine did that it turned out to be the clamps on the short hose on the water pump were a little loose. Replacing the cap also won't hurt.

I doubt it is the head gasket but you never know. I just changed the oil and it looked normal. I will check the weep hole on the water pump. I have added straight coolant sometimes so the ratio is close. The glycol does not evaporate so normal topping off of the coolant should just need water unless there is a leak which sounds like my problem.

After I check the weep hole, I might drain the system and do a pressure test and change the thermostat.

Can someone confirm the vent tube on the reservoir is suppose to be open and hang down underneath it?

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85 300D Turbo

Yes that is correct, and if you see evidence that coolant is escaping through that hose (without overheating) you need to replace you cap.

yes, there should be a small line off the neck of the filler cap that routes under the tank to the fenderwell. not to be confused with the small line that goes from the top of the radiator to the top of the tank.
John

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

A bit off topic, but how's that Astro with the 450k on it doing...? I just read that and laughed so hard. I thought it was a joke..450k out of an Astro? You must be doing something right.. It's not still on the original...anything is it? Just curious. I've never seen an Astro, or older G.M. small engine/mini type of thing go that long. I find it rather amusing. You should call up GM, and see if they'd like to buy it back. They do that with high milers. I don't know what exactly it is they do with them, but I think it's something in the R+D department.

starts and runs great, original motor only. several new PS pumps, water pumps, alternators, starters, front motor plate accessory brackets, transmissions, rear differentials, door handles, etc. etc. yeah, R&D on how to stop it from getting such high mileage!
really, check out astrosafari.com, the astro when well cared for will never die.
John

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Even having driven in 52C weather in the Rajasthan desert here, I had no issues of the temp needle going over 81c, also no need for top up for the coolant, only every six months do I have to top it up and that too very little.

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99 Gurkha with OM616 IDI turbo

2015 Gurkha with OM616 DI turbo

2014 Rexton W with OM612 VGT