Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

[Big Bubba]

Hello Everyone,
I have a question for you. I own a 2000 year, C3500 Chevy 7.4 liter engine and the only time this happens is when it is hot outside and I have my air conditioner on. Anyway, what is happening and it only happens when it is hot out and my air conditioner running that when I stop I notice that my recovery/expansion tank has coolant overflowing out of it. I do notice that when it sits a while and the truck is cold that my water pump bypass rubber hose going to the lower intake manifold leaks a very, very, very little bit and I have replaced it and I have tightened it down as much as I can and it steel leaks a very, very, very small amount of coolant. I have already in the past replaced the lower intake manifold gaskets and they look dry at all four corners so I am certain that the bypass hose is leaking very very very little and my hose doesn't have any cracks and cuts on it because it is brand new. Could that small leak in the bypass hose cause my coolant recovery tank to overflow only when my air conditioner is on and it is hot outside? Other than that and I drive it without the air conditioner it does not do it. What do you think? One more question, how the heck do I get that pesky bypass hose to stop leaking it doesn't leak a ton of coolant just a drop or two of coolant but enough to drive me crazy and can that outlet on the lower intake manifold where the rubber hose connects to from the water pump be out changed easily with the lower intake manifold on the truck. I do remember it being rough and not smooth where the hose slides over that area. Maybe being rough is causing sealing issues for that rubber by pass hose.

 

[Scott Danforth]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

Has it always done it? If so - My first thought is not enough expansion volume in the factory tank. 7% expansion volume is the minimum.

 

[MTboatguy]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

It is really not uncommon for a overflow situation when it is warm outside and you are running the AC, in fact it is pretty common. The extra loads introduced create a situation that can warm the engine up pretty good. Overflow is not always bad, watch a NASCAR race, the more load you introduce into an engine, means that much more heat has to be dissipated and the only way it can do that, is heating the cooling fluid up. Now when water or coolant boils, it expands, so if it is expanding, then it is going to find a way out. This is the reason, overflow systems still have a overflow hose.

 

[GA_Boater]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

Pressure test your radiator cap. A weak cap will vent to the overflow when it runs hotter due to the condenser adding heat to the radiator airflow.

 

[MTboatguy]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

One other thing, you might take it to a Rad shop and have them make sure it is not the radiator itself, I know I have mine cleaned every 5 years and it helps maintain a full flow.

Looks like you have had this problem for a while, I found another thread you were talking about this that was back in September? After reading through that a bit, again, I would suggest having the pro's at a rad shop take a look, they might be aware of situations with certain models of your truck.

 

[Big Bubba]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

MtBoatguy and GA Boater,
Yeap, I have alot of garbage inside my radiator that looks like rust right now so I want to flush it out again since the last time I flushed my radiator was about September 2012 last year. I will replace the thermostat and its gasket while I am doing that since it was never done since I got the truck last year. Then if that does not cure it after the flushing out the radiator and installing new thermostat then I will get the radiator checked or I might buy a brand new radiator and replace it myself. But like I said there is rust looking stuff floating around inside the radiator right now. Now what I did last september was give the radiator a good flushing and I poured in a bottle of Prestone radiator flush but I never drained the Prestone flush out and redid the flush again after ward so it might have lossened up more crud inside the radiator and that is what I am seeing know. Yeap, I know I should have followed up with another flushing but I didn't so shame on me, LOL. But it will get taken care of this weekend. Don't dawg me out to bad, LOL.

 

[GA_Boater]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

Wonder if you have some stopped up tubes. Maybe a rad shop can rod it out and save the price of a new radiator. No pickin' on you - Yet.

 

[Big Bubba]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

GA Boater,
Will they rod out radiators with plastic tanks like what I have on my truck? If they do I might or better yet WILL get that done. The price of a new one is about $200.00 so if the Radiator shop can rod mine out that would be Great!!! if it is alot cheaper than purchasing a new one. Thank you for the suggestion.

 

[GA_Boater]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

That's a good question. I've only had it done on soldered metal tanks. I know a plastic tank is held on with a crimp band - No idea if it's possible to re-crimp or get new bands. It's worth a call to a shop to find out.

 

[Scott Danforth]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

aluminum radiator and plastic tanks are cheep. about $130 online

 

[Big Bubba]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

Yeap, I found one on eBay, 1994 1999 Chevy GMC K10 K3500 Pickup Cooling Radiator 7 4L V8 TOC Suburban C2500 | eBay, that I think I might get since they are really high at the local Advance Auto Parts store.

 

[hungupthespikes]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

+2 on the radiator shop. Look for one that can back flush. You have a heater core that has the same junk running in it.
A good shop will back flush until all that junk is out of the entire system not just the radiator.

 

[GA_Boater]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

Yeap, I found one on eBay, 1994 1999 Chevy GMC K10 K3500 Pickup Cooling Radiator 7 4L V8 TOC Suburban C2500 | eBay, that I think I might get since they are really high at the local Advance Auto Parts store.

That's a good price. And free shipping too.

Spikes idea about back flushing is a good one. Toss in a new rad and the crud from the rest of the cooling system is gonna end up in that nice, new, clean radiator. Worth considering.

 

[Big Bubba]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

/////////UPDATE///// I think I have found out why my truck's expansion tank keeps overflowing especially when I have my air conditioner running and have stopped my truck. well, I could not believe my eyes when I took a peek between the back of my air conditioner radiator and the front of my engine cooling radiator. I found a 17 inches long by 10.5 inches wide bud light card board box top sitting directly in front of my engine cooling radiator so with finding that card board box blocking the flow of air flow into the engine especially with the air conditioner on I think that caused my truck to overheat and fluid flowing out the expansion tank when I stop my truck and it sits for a bit.

 

[rockyrude]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

Really surprised that didn't show up on the temp gauge.

 

[Big Bubba]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

rockyrude,
It did yesterday show up on the temp guage. When I saw it I almost had a heart attack and immediately pulled the truck to the side of the road and shut her down. I didnt realize till today that the card board box was sitting directly in front of the engine cooling radiator. I guess the reason the guy before me had the truck he had heating issues with his heater warming up but I fixed this issue earlier this year around January that my heater core was clogged up and I flushed all the brown garbage out of it until clear water came out and have not had any issues with the heater not working in fact after a while on high heat it will almost run you outta the truck it gets so warm.

 

[GA_Boater]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

That's amazing, Big B. Never mind any advice I gave. :embarassed: I wonder if the truck heater will be too cold come winter. Way back when, we used to put some cardboard in front of the rad so it ran warmer for heat.

EDIT - I was typing that mess while you were posting.

 

[MTboatguy]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

Where in the hell did that truck come from, I know we run cardboard in front of the rads in winter around here, it is really quite common, but this is quite amazing.

 

[Big Bubba]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

Yeah, I live in Upstate South Carolina and did an even trade with my 1999 Chevrolet Silverado 4X4, 1500, 5.3 liter engine extended cab short bed truck for this 2000 Chevrolet dually, 3500, 4 door, truck with 7.4 liter engine, long bed. The reason I did the even trade is because first off my Silverado was too small of a truck to tow a 30 foot fifth wheel and second my Silverado is starting to show rust bubbles in the paint above the wheel wells. I took it for a drive today to the grocery store to pick up some food for the house and she did good, no problems today. Yesterday, after I let it idle for a while did go a little above 210 degrees on the dash thermostat and started the overflow thing again. I think the reason it did that is because I did not burp the system the first time after discovering the card board box sitting in front of my radiator. What I did was just add water to fill up the radiator and forgot about it and never bleed the air out so I am thinking there was some air pockets in the system cuasing the temp to rise above 210 degrees and the expansion tank bubbled and overflowed coolant. What do you think??? Think I am correct or not???

 

[Grub54891]

Re: Why does my 2000 year Chevy C3500 truck recovery tank overflow only when A/C on?

Just for peace of mind,I would pressure check the cooling systym,thus making shure its not leaking,or bad head gasket causing the issue.
Grub