3800 swap coolant overflow. (Page 2/3)
Darth Fiero OCT 12, 11:27 PM

quote
Originally posted by AL87:

and I just noticed something on my gt when I topped off my coolant recently.
I just got a new radiator cap on there, and made sure it wasn't leaking, but with the car cold, if I take the thermostat housing cap off and take the thermostat out, and "top off" the coolant until it spills over, out of the housing, the coolant flows down into the overflow tank. out through the radiator cap, that isn't supposed to be possible, right? I just got a new cap as well...



All modern radiator caps that work in the Fiero radiator have a small check valve on the bottom of them (dime sized disc) that is supposed to block low pressure coolant flow out of the radiator into the overflow tank, BUT allow coolant flow from the overflow tank into the radiator, if needed. The cap should pretty much block all flow out of the radiator until the rated pressure reading (printed on the cap) is reached in the cooling system (at which point it will allow coolant to flow into the overflow tank). If you are attempting to fill a Fiero cooling system and notice the coolant is just running right into the overflow tank with the radiator cap properly installed, then you probably have either a dirty or defective radiator cap and need to clean or replace it.

[This message has been edited by Darth Fiero (edited 10-12-2014).]

2002z28ssconv OCT 13, 07:23 PM
I say, try replacing the cap first if he hasn't done that recently.
We had a spell here locally where Autozone was selling the wrong cap to us too. Be sure you are getting a non-vented radiator cap. (see correction below)

I have never had a problem burping the air from my 3800 with just the stock 3800 filler neck. It only ran hot the time when the plastic elbow popped out and lost all the coolant.

[This message has been edited by 2002z28ssconv (edited 10-14-2014).]

AL87 OCT 13, 09:58 PM

quote
Originally posted by 2002z28ssconv:

I say, try replacing the cap first if he hasn't done that recently.
We had a spell here locally where Autozone was selling the wrong cap to us too. Be sure you are getting a non-vented radiator cap.

I have never had a problem burping the air from my 3800 with just the stock 3800 filler neck. It only ran hot the time when the plastic elbow popped out and lost all the coolant.



I guess we both have to replace our caps!
weirdest thing for me though, that the cap seals fine and nothing comes out during normal operating

the correct cap, its the one with the spring on the inside, that doesn't have the red lever on the outside, right?
Darth Fiero OCT 13, 10:38 PM
I use the lever vent caps in all of my vehicles (including my Fiero). Never had a problem SO LONG AS I made sure the lever was fully seated in the slot cut for it in the radiator cap. It is possible to misalign the lever with that slot (you can't really see with the lever down) which would prevent the lever from fully closing - which would hold open the overflow tank passage.
2002z28ssconv OCT 14, 08:42 PM
Since yesterday I have done some more research here. The original Fiero cap may very well have been a vented cap. In that case, the statement I made yesterday would have been incorrect. But the info I based that comment on came from people in my local club with a lot of mechanical knowledge and experience. So what is the difference?

First off, the lever is an option on both types, vented and non-vented. Forget about the lever. If you like the lever, get the lever. If you don't like it, get a plain smooth top radiator cap.

Vented... This type of cap will allow coolant to be sucked back in from the non-pressurized coolant recovery tank as it cools down.
Non-vented... This type of cap will NOT allow coolant to be sucked back in from a non-pressurized coolant recovery tank as it cools down. I think these are made for cars with coolant recovery tanks that are pressurized. Using this type of cap may make it more difficult to get all the air burped from the system too.

From poking around on the web it seems that people find more failures with the vented cap when they don't seal back up after the cool down process. When this happens, coolant will be quick to boil out into the recovery tank when the engine reaches operating temperatures. That must be why my local gurus said to put in a non-vented cap when we were troubleshooting a club member's car that was prone to overheating.

If you have a cap with lower pressure setting it will also be quick to boil over. If the car is boiling over before the engine temp gauge says it is overheating, you have a pressure issue. It can be a defective or weak cap or it can even be a head gasket issue where the pressurized exhaust gas is inflating the cooling system. We had that issue in my daughter's 99 Buick Century.

Anyway, I wanted to clear that up as I gave somewhat incorrect information there.

Look for a V on the cap like this one...

[This message has been edited by 2002z28ssconv (edited 10-14-2014).]

AL87 OCT 16, 12:32 PM

quote
Originally posted by 2002z28ssconv:

Look for a V on the cap like this one...





I have that, but not vented. do you have the part # by any chance?
Darth Fiero OCT 16, 08:09 PM
Non-vented radiator caps were made to be installed on radiators that did NOT have coolant overflow tanks (old cars, mostly) AND are also used on specially molded overflow tanks that hold cooling system pressure (usually found in newer cars that did not have a radiator cap on the radiator itself).

All Fiero systems have overflow tanks that are NOT pressurized, which means they must use a "vented" cap installed on the radiator. Sorry if I added to the confusion concerning my comments about the LEVER-VENT radiator cap (which has a lever installed on the cap so you can vent pressure without removing the cap).

If you need a vented cap (with a lever or not), just go into any parts store and have them look one up for a stock Fiero. It'll be the correct one to use with a 3800 swap.

[This message has been edited by Darth Fiero (edited 10-16-2014).]

1fast2m4 OCT 18, 09:48 AM
I do not have a dedicate water fill point in my engine bay. I just pop the hose off he T-stat housing fill it up as much as I can, then start the car and once it starts to warm up I crack the bleeder open on the 3800 T-stat housing until coolant squirts out. I've never had a problem.

------------------
1986 SE 3800SC/4t65eHD (12.871@104.96)
HX-40, FrozenBoost I/C, 80lb injectors & E85 Coming soon.....

1fast2m4 OCT 18, 10:03 AM
Ooops....

[This message has been edited by 1fast2m4 (edited 10-18-2014).]

Darth Fiero OCT 20, 03:36 PM
On all the 3800 swaps I do, I set up an engine coolant fill point that connects to the heater hose return port on the water pump/alternator bracket. I only use the stock 3800 t-stat housings because the modified Fiero t-stat housing is huge, ugly, and sometimes has issues with t-stats getting bent up in it.