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Engine Specific Info and Questions => IDI Engine => Topic started by: overdrivegear on June 07, 2010, 06:21:04 pm

Title: cooling system pressure and expansion tank cap
Post by: overdrivegear on June 07, 2010, 06:21:04 pm
It was recently brought to my attention that I should not use a black expansion tank with my diesel.  I did a 1.6 NA swap into a cabriolet (videos here):

1987 VW Cabriolet 1.6 Diesel engine running pt. 1 (http://www.youtube.com/watch?v=MF_e1oen20A#)

1987 VW Cabriolet 1.6 diesel running pt. 2 (http://www.youtube.com/watch?v=3QrsopfQO4I#)

and I just kept the gasser expansion tank and cap.  Someone told me that if I keep that black cap, I will run the risk of blowing a head gasket ???
So my questions are, does the color of the expansion cap make a difference and if so what cap should I use?  Do these coolant caps actually vent pressure according to their color?  I was under the impression that these caps didn't vent pressure at all.

Title: Re: cooling system pressure and expansion tank cap
Post by: GEE-BEE on June 07, 2010, 07:29:11 pm
I installed the later round type tank....

 non sensor

GB
Title: Re: cooling system pressure and expansion tank cap
Post by: the caveman on June 07, 2010, 07:36:45 pm
The caps will vent , although only at higher pressures than normal-i.e. when you're overheating, so no, not in a normal fashion. In that case, i don't  see why a different cap pressure would make a difference, but i would try to find a definite answer if you're having issues.
Title: Re: cooling system pressure and expansion tank cap
Post by: overdrivegear on June 07, 2010, 07:45:31 pm
The caps will vent , although only at higher pressures than normal-i.e. when you're overheating, so no, not in a normal fashion. In that case, i don't  see why a different cap pressure would make a difference, but i would try to find a definite answer if you're having issues.

I'm not having issues.  I just wanted to avoid a noob mistake with the wrong 'cap pressure'.  Kinda sounds silly, but then again there is a fair amount of silly business with these Volkswagens and I wouldn't put it past them.
Title: Re: cooling system pressure and expansion tank cap
Post by: Baron VonZeppelin on June 07, 2010, 09:20:55 pm
I'm gonna say .... ol wives tale.  ;)
[but reserve the right to be wrong]

Maybe should send this in to MythBusters.

I believe they will vent in the high teens-20'ish, but never seen black or blue listed as gas or diesel specific - or even listed with a psi rating. So figured they were the same other than color of the plastic.

I have both color caps amongst my a1/a2 diesels.
I think the score is 3 black and 2 blue, on my fleet.
Title: Re: cooling system pressure and expansion tank cap
Post by: one_tinted_tail on June 07, 2010, 10:39:48 pm
sounds like bumper fluid talk as well, and I like the reservation of right to be wrong, HA!

they pop at extremes, yes, but not aware of color/pressure differences.