engine and drivetrain Coolant Overflow Problem

[mikethevilla]

Hi Folks!

 

There have been some weird happenings with my cooling system, so I once again am here to solicit the advice of people who actually know what they're doing (or at least are good at pretending they do).

 

My '72 is fresh out of rehab - all new upper gaskets, redone head, new cam... Solid professional top end rebuild. Everything is running great, but every so often my radiator will start spewing coolant from the expansion line. The radiator is some form of E21 part that the previous owner put in. It's a bit rough looking, but I just had it pressure tested/leak down/whatever they do to check radiator things and I got the all clear.

 

The weird part is that my temp gauge never gets warmer than about 2/3rds of the way up. I haven't done any kind of extended commuting or hard drives yet, but during normal driving temps are running at about 3:30 (lower than they were before the rebuild), and during harder driving or stop and go it might hit 3. As those in SoCal know too well, the past couple days have been uncomfortably warm (+85º) and driving in rush hour or idling for 5-10 minutes bring my temp up to about 2 o'clock on the gauge. At that point, it starts peeing coolant all over whatever parking lot I happen to have ended up in. Again - temp is warm, but nowhere near the red.

 

My first thought (and hope) is that I have a bad radiator cap. I'm assuming tension springs could go bad/get loose and let out the coolant too early?

 

My second (and slightly more worrisome thought) is that my temp gauge is wildly off and that my car is actually overheating. I'm running that old E21 radiator and a stock fan so that seems entirely plausible, but my temp gauge has been fairly reliable, so I'm not sure. Also of note: I haven't yet done final tuning since the rebuild, and so timing could be off and contributing to temp creep.

 

Ok. Bring on the conspiracy theories.

Oh. And related: I'm now taking expansion tank recommendations.

[pklym]

Get an IR thermometer and try to learn what your actually temperature is. And spend $10 on a radiator cap, but if it is the temp sensor then I wouldn't want to replace the cap and just wait to see if it happens again (while frying your engine).

[tups]

pklym's thoughts are my thoughts exactly - the cap must be bad, but if something more sinister is going on, then you definitely want to know about it - have a thermometer handy when it happens again, and check temperatures of the radiator top regularly. IR thermometers these days are cheap, 2002 heads and rebuilds aren't !

[Zorac]

i had a similar problem, turns out i was just over filling it.  if i fill it to the brim, it spews until the top storage area of the rad above the fins is about half full, then its stops spewing and is fine

[Simeon]

I would be concerned about head gasket failure pressurising the cooling cooling system. Go and find someone with a cooling system tester. This should be able to test the blow off pressure of the cap and installed on the radiator it should show you what is going on. If the system pressure is getting above the correct cap pressure, particularly if only warm then your head gasket may be at fault.

[TobyB]

I like the overfill theory. 

On the E21, there's a plastic 'ledge' about an inch and a half down

that you're supposed to fill to, but not over.

 

But put a bike water bottle on it and see how much you're getting....

 

t

[jrhone]

when you look not the radiator when cold…where is the coolant level?  Is it all the way full or about an inch low.  An inch low is the normal level.  If higher then its overflow.  If its lower than an inch, and you can see the cores then you are low and you are spewing coolant when you shouldn't.  

[mikethevilla]

Thanks guys. Took a look this morning and coolant looked a little over 2" from the radiator cap, maybe .5" from the core (I could clearly see the top). Took a look at the cap as well, apparently it's a 14lb cap (which might be a bit weak?).

I'll keep an eye on things and pick up a IR thermometer sometime this week.

Sent from my iPhone using Tapatalk

[Hans]

I'd be trying a different cap.

[jimk]

apparently it's a 14lb cap (which might be a bit weak?).

This system was designed for a 13psig cap, so 14psig should be ok.  I wouldn't add pressure with a higher pressure cap, you might start blowing hoses, gaskets, etc.