Coolant Reservoir Tank Cap Question 1990 4.0

[AnotherOldJeepGuy]

I just swapped out my coolant reservoir.  I think this might be the 4th time over the years!  My question is about the cap.  I adding in a picture of the old split cap, as well as pictures of the old very bloated tank and the new one.  The old tank swelled up a couple years ago, I think this was a result of overheating (which was due I believe to insufficient coolant because the folks that swapped in a new radiator didn't burp it well., but I managed to get it burped and the overheating stopped).

 

Anyway my real question is about the cap.  The split open open one has an obvious pressure release, but the new cap doesn't particularly look like it does.  The new tank is Dorman 603-300 purchased a few years ago when I knew I'd need it sooner or later.  The last time I replaced this tank, it had the same black cap but I didn't use it, opting to reuse the one from the one before that, the one that has now split.

 

Is this new cap also designed to let off excess pressure but just doesn't look like it?  If the answer is NO, can anyone direct me to when I can get one like my old one?  I do see that every Dorman 603-300 I can find online now has this same black cap.

 

Oh, my other question is, that is the metal threaded orifice/port on the top of the tank used for?

 

 

 

 

 

[fiatslug87]

That black cap is fine. That’s what my ‘90 had when I purchased it new. I think the one that split is a different aftermarket one.

I’ve seen some ‘87s in the junk yard that had a bracket attached to that threaded piece instead of the strap.

[NC Tom]

FWIW: Cruiser54 recommended this, "Get a 703-1396 cap from Napa or an equivalent. From a Volvo."

I did, and it works really well. Holds tight.

[89 MJ]

3 hours ago, AnotherOldJeepGuy said:

Is this new cap also designed to let off excess pressure but just doesn't look like it?  If the answer is NO, can anyone direct me to when I can get one like my old one?  I do see that every Dorman 603-300 I can find online now has this same black cap.

 

I ordered the Dorman one and used the cap a few years ago. My tank let go, it wasn't the cap that let go from the pressure. That could've just been a bad tank though.

[AnotherOldJeepGuy]

I attempted to determine if the cap was hitting the hood with a propped  up piece of masking tap on the cap and closing the hood.  I don't think it is touching, I am pretty sure the old one did a little because of the bloated tank.  I read that the Volvo cap is lower profile, but it's also closing in on $20 at this point, so my plan is to monitor for a little while and if no leaks are seen, leave it alone.  If I see leaking I might go ahead and get the Volvo cap and see what happens.  If I learn anything useful, I'll post it.

 

I saw on a different forum that someone lowered the tray a little for clearance to the hood, I have wondered about this myself but have not pursued it, yet 

[pizzaman09]

The best combo I found was the doorman tank with the original black cap.  The cap with the brown vent just wouldn't hold pressure for me for the three different tanks I went through.