I just converted my closed circuit cooling system in my 90 to an open system and when I key off and let it sit it is pissing coolant from the overflow nipple. What do I need to do to stop this? I'm thinking the cap may be weak

 

An "open" cooling system MUST allow hot coolant to escape. The rad cap is the key component in a properly functioning "open" cooling system. The "open" system rad cap has 2 valves and 3 sealing surfaces.....all of which must function properly. It also MUST have the coolant escape tube plumbed from the cap to the BOTTOM of the coolant recovery bottle. The bottle MUST be "open" to the atmosphere.....NO pressure build-up in the bottle.

 

Like said, that nipple should be in a hose that goes to the bottom of a reservoir who's top it roughly level with the cap. (1/2 gallon should do). As it cools, vacuum from the cooling system will draw coolant back through one of those valves DJB mentioned, back into the radiator.

My Jagurlet (Jag/Chevy 350), has an inline pressure cap, I just ran the overflow/recovery tube into a quart oil jug, actually works OK. (You gotta use a Castrol 30W jug though)

What do you think DJB..18# cap for that? (or 16)

 

Ok well I guess all my old chevys have been broken in the past then they didn't have a recovery tank and never pushed or pulled coolant out. It was a surprise when I turned it off that it was leaking. I don't have a recovery bottle yet I have a factory one but its too big to put anywhere under hood

 

Must have been really old Chevy's because the '74 Chevy Monte Carlo I bought new in '73 had a "open" cooling system which had a coolant recovery bottle. Hot coolant level in the bottle would be +/-1"-2" higher than when the motor was cold. As the motor cools (say overnight), the coolant level in the bottle dropped that +/-1"-2" as coolant was drawn from the bottle, back into the rad. That's the way a properly functioning "open" coolant recovery system works. Again, a properly functioning "open system" rad cap is the key component. If coolant does not escape from the rad into the bottle when hot, then the rad/cooling system is low on coolant. That lost/low coolant is replaced with air....and that ain't good.

 

Like I said it must have been broken or wrong. I had 2 66 c10s a 77 80 79 c10 and none had a recovery bottle when I got them and none over heated or leaked coolant except the 80 as the radiator had a hole in it

 

They also had a cooling system far more capable of cooling the motor.

The XJ cooling system is .... Adequate to the task ... if in prime condition.
The system is designed to have an expansion bottle and actually needs it, as it heats up it will push a couple litres out due to heat/pressure expansion. As it cools it will suck that back in.

The old trucks/cars had a recovery bottle, there just to keep the EPA off there butts . If you leave the level 1" below the cap, you allow expansion room and almost eliminate loss. Can't do that with the XJ or you've be likely to run hot.

 

Definitely broken/wrong. I doubt any C10, F100 or D100 1/2 ton p/u had a 10,000+ lb tow rating like most 1/2 tons of today. Much, but not all, of todays increased tow capacity is due to modern cooling systems being much more capable than "old school, back in the day" cooling systems. I believe at least some coolant recovery systems with bottles were in use before the EPA was established. What vehicle, in say the past +/-45 years, has not used a coolant recovery system and bottle? The really old school +/-1" air space/gap in the top of the rad and no recovery bottle design disappeared a long time ago. Old school design cooling systems (with air in them) are way more inefficient/less capable than modern design (airless) cooling systems.

With regard to the cooling efficiency/performance of modern "open" and "closed" cooling systems, neither has a cooling advantage over the other. One is no better than the other at keeping the motor cool, presuming both r in top notch condition.

 

Ok well I just pulled in the driveway and the neck cracked on my radiator. I have two options go back to the closed system or get a new radiator. Problem is there's so many different options what one do I need.

 

Since u "just converted", use your warranty and get a new rad.

 

Warranty is non exists t for a part that came with the jeep when I bought it and it came from a parted out jeep. So yeah

 

Got our new rad at AutoZone......$110 iirc, lifetime warranty. That was 4+ years ago and all is still good. Again, there is no cooling advantage, "open" vs "closed". U make the call.

 

I tossed the metal lines for the closed system and our trash at the shop is taken out tonight I think. Did yours have the hole for the e fan switch

 

Negative....the efan sensor on a '98 is in the t-stat cover.

 

I want just a direct swap like this one was everything is in the factory spot