Strangely enough, my E300D doesn't get very high pressure even when the system is hot. Usually I can still fully squeeze the hose. But forget squeezing the hose on any of my other cars that I've had. Typically it's almost rock-hard when the engine is hot, but there's zero pressure or slight vacuum when cold. It's like there's less room for the air to expand compared to my E300D.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

just to jump into the fray, i've got an 86 w126 with a 603 engine, and it definitely does have the overflow tank hidden in the fender. Seems inconvenient... half the car seems to have to come apart to drain the thing if you ever did boil one over enough to fill it up

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

It's DONE



-either the gasket is toast, or the head is warped/cracked.

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-1983 VW Rabbit LS Diesel (5speed, VNT/Giles build)

Now this is weird. Lately (as in this week) I've been having a slight vacuum after cool-down. I'll take that as a good thing, but I have no explanation for it.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

Same here, with my new #22 head. AFAICT that is kinda normal on a 60x. For a while I was trying to "fix" it with new radiator caps, burping, etc but I finally accepted it as normal. Haven't had any issues since (and ZERO cold pressure.)

That's why it's advisable to do the coolant CO2/HC test. Dealership shops will not take a suspect head/gasket off without one.

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1987 300D (230,000 mi on a #14 head-watching the temp gauge and keeping the ghost in the machine)
Raleigh NC - Home of deep fried sushi!

This might just be a wild idea but I see you are in Sparks, Nevada so by any chance are you filling the system and then checking at different altitudes. I don't know the altitude around there but I would guess that it varies.

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1983 300SD
200000miles

Phil, I always check the system at the same place (my garage) and similar if not the same temperature. I'm well aware of the roles that atmospheric temperature and pressure play here and I try to eliminate those variables. What's strange is that until recently I had small residual pressure. Now I have small residual vacuum and I can't blame it on the weather. I'll keep checking.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

I guess you are to far from Area 51 for that to explain it
Interesting problem. What happens if you run it with the cap loose, do you see any bubbles or vapor? I wonder if the hose from the radiator to the overflow tank could be restricted in any way to cause the tank to hold pressure. I can understand the tank having a vacuum after the system cools but some times having pressure is something new. Kind of far fetched but I do remember a situation where I had a pipe that had something cought in it that acted like a check valve.

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1983 300SD
200000miles

No bubbles in the coolant reservoir. I don't think it's possible to see bubbles there since it's so far away from the head. More likely you'd have coolant overflow if there was a lot of gas buildup in the cooling system. The hose obstruction actually doesn't sound too far fetched to me. I did flush the overflow hose and filter the coolant after messing around with some of the head gasket repair products a few months ago, but it's possible I still have a few leftover chunks circulating with the coolant. The only problem with that theory is that the residual pressure was the reason I tried those products in the first place, i.e. the pressure came first. As I mentioned in another thread, the product mostly eliminated the pressure, but not completely. Last week I brought my car in to an indy to have my lower control arms replaced and ever since then I've had vacuum in my cooling system , despite me resetting the pressure afterward to eliminate the possibility of the mechanic having messed with my coolant cap. Either the mechanic secretly replaced my head gasket for free, or I'm still too close to Area 51.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL