Pressurized 'surge' tank vs overlow bottle..

[rcy]

The new Equinox has a pressurized 'surge' tank with the rad cap on the tank instead of the rad. This is a new design to me - all other vehicles I've owned having a coolant overflow bottle that was not pressurized.

What's the reasoning behind this type of system? Is it to prevent Dex-Cool from reacting with air?

 

[Colt45ws]

I think it is more of an environmental thing. But preventing air getting into the system is a side benefit. Pretty much every vehicle that is noted to have issues with DexCool has a regular overflow bottle.

 

[HTSS_TR]

My 1994 Lexus LS400 has pressurized plastic reservoir, the coolant cap is on the reservoir not on the radiator. Overtime the plastic reservoir develop a leak near the coolant temperature sensor. My 2000 MB E430 has the same design. The pressurized plastic reservoir is not a good idea. The old design, the cap on the radiator, is better.

 

[Colt45ws]

Hmm, Only issue Ive ever had with them is the cap developed a leak on my old Cavalier. But that was simple. Trying to thread a metal object in to a piece of plastic that gets hot and pressurized does sound like a bad idea to me though.

 

[eljefino]

It's a system design thing, the rad can sit lower than the engine's high spots. Put a thin outgas hose on the top of the motor where you'd otherwise have a bleed valve and it's self-burping.

Seen similar systems on 1960's hot rods: remote pressurized outgas doohickies. Of course made of all metal.

 

[onion]

All modern heavy trucks have essentially the same setup. Like eljefino said, it allows the radiator to sit lower than the engine (doesn't require it, but does allow it), continuously bleeds air from the engine and radiator, and allows the ACTUAL coolant level to be visually checked without removing the cap (as opposed to just the level in the overflow tank).

BTW- though this setup does generally work better with Dexcool (less likely to let air into the system, less likely to be driven underfilled for an extended period), it's no panacea. Lots of small, cheap GM cars have had this system since the mid-90's... maybe earlier. And they were not immune to Dex-sludge- particularly if they had a 3100 or 3400 engine.

 

[mechanicx]

Very good points. GM had some models that had the pressurized reservior since at least the late 80's and early 90's with Green and well before Dexcool came on the scene. I would question weather all alumninum engines or the bimetal 3100 and 3400 with a pressurized reservoir sludged with Dexcool. About the only time you'd see that is if the IMG leaked and the owner allowed the coolant to go way low. You didn't even have to get low coolant really to get the cap on the radiator and all iron engines to sludge.

I slo think the pressurized reservoir system lose less coolant to evaporatation from the reservoir than the cap on radiatorstyle.

 

[Coolant_Man]

Pressurized is better for numerous reasons already listed here. I still open mine to visually see the coolant and smell it.

 

[SteveSRT8]

Originally Posted By: HTSS_TR
My 1994 Lexus LS400 has pressurized plastic reservoir, the coolant cap is on the reservoir not on the radiator. Overtime the plastic reservoir develop a leak near the coolant temperature sensor. My 2000 MB E430 has the same design. The pressurized plastic reservoir is not a good idea. The old design, the cap on the radiator, is better.


Come into the new millenium, old timer!

There's been a few advances in technology since '94!!!

 

[George7941]

Originally Posted By: HTSS_TR
My 1994 Lexus LS400 has pressurized plastic reservoir, the coolant cap is on the reservoir not on the radiator. Overtime the plastic reservoir develop a leak near the coolant temperature sensor. My 2000 MB E430 has the same design. The pressurized plastic reservoir is not a good idea. The old design, the cap on the radiator, is better.


The sensor is likely a coolant level sensor and not a coolant temp sensor. Never seen a temp sensor on the surge tank.

 

[Steve S]

It is not a new idea 1960s cars had them, do a search on BITOG for pics this has been discussed before.

 

[Drew2000]

Ford calls them a "de-gas bottle". The coolant circulates through the bottle and any dissoved air in the coolant is continuously purged.

 

[38sho]

I don't like the pressurized tanks

not made of plastic anyhow..... just doesn't seem like it is going to be a good thing for longevity....

also if your regular overflow bottle breaks, its not hard to rig something up in its place, I've even used a gatoraide bottle once. But with a pressurized tank, you usually have multiple different sized coolant hoses comming from it, and they are usually molded to a certain area of the car... so when they break, you need another exact replica......

 

[MNgopher]

Depends on the setup. My '88 Cherokee has the pressurized system, and it is a pain to keep it happy. This was used on '87 to '90 Cherokees with the 4.0 and it was replaced by a traditional system. Switching to the traditional system is pretty normal for Cherokees from this era. The main problem is the bottle and cap. The bottle tends to crack and the caps are fickle. I've still got it in my '88, but it is on the 4th bottle in the past 7 years. All replaced preventatively, not a failure.

On the other hand, the pressurized system on my '99 F150 has been fine, and was fine on my '97 F150 as well. No issues to report 180,000 miles later on the '99...

 

[MCompact]

BMW first started using a pressurized system in their E3 sedans(2500, 2800, 3.0si, Bavaria) in the late sixties:

The system uses one or more bleed screws, depending on the series and the engine.

BMWs from the early '90s onward attach the pressurized expansion tank to the side of the radiator, leading many to believe that the expansion tank is the radiator's side tank. Nope:

 

[George7941]

Just because the surge tank is made of plastic does not mean that it is prone to cracking, it depends on the quality of manufacture of the tank.

At work we had a 1997 diesel Chevy van go 10 yrs/ 280k mi with no problems at all from the plastic surge tank. On the other hand, the metal surge tank on a 1999 Freightliner truck corroded and started leaking in 2008. i paid about $130 for a new surge tank.

Here is a pic of the surge tank on my Sierra (still on the factory fill of Dexcool)

 

[mechanicx]

Exactly that the pressurized reservoir is made from translucent plastic doesn't really matter, because most radiator are made from plastic as well and that doesn't mean they will necessarily be more leak prone or crack. Besides a non-pressurized reservoir could be cheaply made too and crack and leak and you'd be no better off.

 

[440Magnum]

Originally Posted By: rcy
The new Equinox has a pressurized 'surge' tank with the rad cap on the tank instead of the rad. This is a new design to me - all other vehicles I've owned having a coolant overflow bottle that was not pressurized.

What's the reasoning behind this type of system? Is it to prevent Dex-Cool from reacting with air?


Its a fairly old design now- Jeep Cherokees had it in the 80s, my wife's 93 Vision TSi had that design.

It works well, really minimizes evaporative loss from the cooling system, minimizes air exchange (keeps oxygen out). It also circulates coolant through that tank constantly, unlike "open" systems where the tank only gets a squirt of excess coolant as the engine heats up and then draws a small squirt back into the engine as it cools down. Open systems also quit exchanging coolant with the overflow bottle AT ALL if there's a small leak high in the system which lets air intrude rather than sucking coolant back from the overflow- which means that open systems have a failure mode where the overflow tank level is right but the radiator is actually very low.

The downside is that when that plastic tank goes "bang" and splits open under pressure, you're stuck until you can get another one. Early Jeep Cherokee owners (for example) consider it a reliability upgrade to convert to an "open" conventional overflow tank system used on later Cherokees. That said, wife's 93 made it to >250k miles without having the tank fail. But it was looking REALLY yellow brittle when we got rid of the car. If we'd kept it, I'd have replaced that tank before taking it out of the city limits. Overall, I prefer the open system because I'm a maintenance freak and check the ACTUAL level in the radiator regularly. But for the "I turn the key and it goes" crowd, the pressurized reservoir is probably a little safer (assuming they ever look at it at all).

Yes, it does work better with DexCool too because it minimizes oxygen intake into the cooling system, but the design itself pre-dates DexCool by 10+ years.

 

[Shannow]

Renault 16s had a glass pressurised surge tank located way, way below the water pump, and the water level was (probably) only just level with the bottom of the block water jacket.

Parents car went 380,000 plus km with no issues. Had to be bled right, but had bleed points at the heater and head.

My E30 has a pressurised plastic tank. Prolly close to 300,000km, and there's no sign of creep (whitening) at the changess in section.

A pressurised tank will continue to feed a coolant leak, while an atmo pressure tank can't "top up" a leak until the system cools and sucks it back in again.

 

[Silk]

Most Euro vehicles have a pressurised surge tank.They always feed into the lower rad tank or bottom hose,and have a bleed hose off the top housing.Self bleeding,and don't blow hot water into your face if they are opened hot.I much prefer them to a cap on the top tank and a siphoning overflow bottle.