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Old 11-16-2012, 11:03 PM   #1
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Default Check your radiator caps?

Last spring, I accidentally discovered we had a bad radiator cap in our 07 Roadtrek with a 6.0 Chevy engine. I was doing the change to the alternator to reduce the charging voltage (new/different regulator) and pushed on the radiator hose to get it out of the way. I noticed that the coolant in the overflow tank moved. That shouldn't happen as it takes 15 psi to open the cap, and the engine was cold, so no pressure. Put on a new cap and all is well, but it was only 13K miles, so the caps may not be so great. We had noticed a tiny amount of water usage just before that, and I was getting nervous about the infamous Dexcool manifold leak issue. The water use went away with the new cap.

Last week, I told pretty much all the home mechanics I know to check their caps by squeezing the radiator hose on their Chevies, mostly pickups. One out of 12 had a bad one. Last year when I did the same, it was 2 out of 14.

So, it may pay for all to check, as it is so easy. Squeeze the radiator hose. The coolant in the tank shouldn't rise. If you want, post what you find, so I can see how widespread bad ones are. In our vans, a bad cap can be a very bad thing. It lowers the boiling point, making them much more likely to puke water and get steam pockets in the heads on long climbs or traffic, and we know the Chevies are borderline already. It also may let air into the cooling system, which is death to Dexcool.
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Old 11-17-2012, 01:05 PM   #2
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Default Re: Check your radiator caps?

Thanks for the info.

I'll check mine today.
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Old 11-19-2012, 04:10 PM   #3
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Default Re: Check your radiator caps?

<<: long climbs or traffic, and we know the Chevies are borderline already. It also may let air into the cooling system, which is death to Dexcool.>>:
Another good tip from Booster - thanks, I'll check mine .
But, wondering why reduce charging voltage of alt.? I've often thought that more was better...
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Old 11-19-2012, 04:26 PM   #4
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Default Re: Check your radiator caps?

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Originally Posted by AZ ADVenturist
<<: long climbs or traffic, and we know the Chevies are borderline already. It also may let air into the cooling system, which is death to Dexcool.>>:
Another good tip from Booster - thanks, I'll check mine .
But, wondering why reduce charging voltage of alt.? I've often thought that more was better...
The Chevy charges at a very high voltage, if it is going to be on the batteries for a long period of time. Ours was running in the 14.5-14.7 range at a minimum. Gassing voltage for wet cells is around 14.1, so the batteries constantly gas. Put that on them for a few 12 hour drives and you have used a lot of water, made a bunch of mess with the vapor, and also shortened the life of the batteries. I have the disconnect set up on a relay so that it only can be used when the motor is running, so we can't forget it disconnected and not charge when we are plugged in, although that may change shortly. We are hoping to do some solar, and I think the solar would also activate the separator. The separator coil pulls 1.5 amps, which is pretty good chunk of solar output, so I think we would need to be able to disconnect then, also.

We currently have a different regulator in the alternator the runs at about 1.38-13.9 volts, so we are less critical now. When we used the disconnect, it dropped our water use by more than 1/2, with the lower voltage it is down by about 3/8, so it is pretty close to being as effective.
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Old 11-19-2012, 04:39 PM   #5
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Default Re: Check your radiator caps?

Thanks, I'll study that a bit more. You mention wet-cell, as I understand to be conventional Lead/acid batteries. But how does that apply to AGM, Optima or Odessey or other sealed batteries? I always use AGM & H.O. regulators in motorcycles. Batteries hold charge & last lot longer.
apples vs. oranges??
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Old 11-19-2012, 04:39 PM   #6
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Default Re: Check your radiator caps?

Thanks,
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Old 11-19-2012, 08:35 PM   #7
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Default Re: Check your radiator caps?

Quote:
Originally Posted by AZ ADVenturist
Thanks, I'll study that a bit more. You mention wet-cell, as I understand to be conventional Lead/acid batteries. But how does that apply to AGM, Optima or Odessey or other sealed batteries? I always use AGM & H.O. regulators in motorcycles. Batteries hold charge & last lot longer.
apples vs. oranges??
As I understand it, AGM batteries like bit less charge and float voltages, but I have no experience with them except for our hotrod with an Optima. The vehicle runs at 13.7-13.8 and down to 13.5 when very hot, so high voltage is not an issue. That Optima is approaching 18 years old.
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Old 11-21-2012, 12:35 PM   #8
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Default Re: Check your radiator caps?

Is there a straight forward way to determine the quality of the batteries for accepting and holding charge? It has always seemed to be a volatile environment. Whenever I check them with an electrical testing meter, mine always look fully charged, but I wonder how accurate that test is? I try to check them after they've sat for a few hours after driving the van for at least 2 hours. Also, wouldn't the amperage from the alternator to the batteries fluctuate with constant changes in engine revs to some extent? So they aren't always getting hit as hard at idle, as they are at freeway speeds? Could that slight rate of charge difference, every so often, mitigate the over charging scenario? I have 2 Deka AGMs that are 2 years old. They've always seemed fine since I changed to them, but we haven't been out this year except day trips, so I'm looking for the best way of evaluating their condition, longer term.
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Old 11-21-2012, 01:08 PM   #9
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Default Re: Check your radiator caps?

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Originally Posted by Mike
Is there a straight forward way to determine the quality of the batteries for accepting and holding charge? It has always seemed to be a volatile environment. Whenever I check them with an electrical testing meter, mine always look fully charged, but I wonder how accurate that test is? I try to check them after they've sat for a few hours after driving the van for at least an hour. Also, wouldn't the amperage from the alternator to the batteries fluctuate with constant changes in engine revs to some extent? So they aren't always getting hit as hard at idle, as they are at freeway speeds? Could that slight rate of charge difference, every so often, mitigate the over charging scenario? I have 2 Deka AGMs that are 2 years old. They've always seemed fine since I changed to them, but we haven't been out this year except day trips, so I'm looking for the best way of evaluating their condition, longer term.
Our 07 Chevy holds the same voltage at idle as it does going down the road, which is much different that the older vehicles that had voltages drop by large amounts at idle. "Back in the day", everyone's headlights were dim at idle. Since the current a battery accepts is based on voltage, I don't think speed would have any affect on charging. What does your voltmeter read at speed and at idle?

I don't know how you accurately check the condition of an AGM, unless you have an amp-hr tester like the one I saw at our local Trojan distributor. It would measure the capacity of the battery by discharging it at the specified rating amp and times that give the original amp-hr rating to the battery. Voltage may be all you have with AGM. Our wet cells allow us to check electrolyte specific gravity, which adds a another level of information, especially concerning state of charge.

Part of this year's improvements is to install a Trimetric battery monitor, which will, supposedly, keep track of amp-hrs in and out of the batteries and give us a real time, accurate, display of what is left in the battery bank. We'll see how well it works next summer. We run a non-recommended mix of batteries (two 260ah 6 volts and one 115ah 12v), so we are concerned about how evenly they charge and discharge. The limited use we did this summer showed no issues, and all of them filling the same, but they weren't cycled much, or deeply, as we usually had shore power.
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Old 11-21-2012, 05:00 PM   #10
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Default Re: Check your radiator caps?

To a charging alternator, or a battery meter, or a Trimetric device, I've always thought the group of mismatched batteries connected in parallel, look like one big battery (by capacity). Whether they're all brand new or different in voltage or charging rates, I've also theorized that if they're connected in parallel (assumption?) they're like a series of different sized cups, like a champagne tower of glasses, and that as each one reaches it's capacity, the current spills over to the next battery in the group until that one is charged, and so on. The rate of draw down might be different, but as long as they're all recharged as a group, it should work. I realize it's a simplistic analogy, but it makes sense to me, right or wrong. And, I've had this discussion on more than one forum. Some opinions are the same as mine and some differ, with the doomsday warnings about new and old, or 6V and 12V, or any other combination that isn't, identical batteries, installed at the same time, built on the same date, etc., etc.....
I'm not sure your configuration as described would/should have any problems, but I'm not an electrical engineer.
I think I'll just go with, my set up seems to work, and I always seem to have battery power available, but we do a lot of driving, so recharging via alternator is fairly regular.
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Old 11-21-2012, 10:24 PM   #11
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Default Re: Check your radiator caps?

Quote:
Originally Posted by Mike
To a charging alternator, or a battery meter, or a Trimetric device, I've always thought the group of mismatched batteries connected in parallel, look like one big battery (by capacity). Whether they're all brand new or different in voltage or charging rates, I've also theorized that if they're connected in parallel (assumption?) they're like a series of different sized cups, like a champagne tower of glasses, and that as each one reaches it's capacity, the current spills over to the next battery in the group until that one is charged, and so on. The rate of draw down might be different, but as long as they're all recharged as a group, it should work. I realize it's a simplistic analogy, but it makes sense to me, right or wrong. And, I've had this discussion on more than one forum. Some opinions are the same as mine and some differ, with the doomsday warnings about new and old, or 6V and 12V, or any other combination that isn't, identical batteries, installed at the same time, built on the same date, etc., etc.....
I'm not sure your configuration as described would/should have any problems, but I'm not an electrical engineer.
I think I'll just go with, my set up seems to work, and I always seem to have battery power available, but we do a lot of driving, so recharging via alternator is fairly regular.
The explanation that I got from Trojan is that different batteries have different internal resistance. The different resistance makes them take charge and give up charge at a different rate. Net result would be to work one battery harder, which, especially when charging could make it boil out water faster and possibly overheat. They also said that one battery may get to voltage and drop the charger down early, but that doesn't seem like it could physically happen. I do think that a lot of the problems being referred to are a throwback to single stage chargers, that held the voltage above the gassing point. I would think 3 step chargers would only have the mismatch during bulk charging and once on float, the batteries would even out without damage. I did talk to Lifeline about it also, and they said recent testing didn't show any problems with mixing. The jury is still out in my mind, but my inclination is that the risk is overblown.
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Old 11-22-2012, 12:46 AM   #12
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Default Re: Check your radiator caps?

I asked several manufacturers and battery retailers/servicers a while back, and also got mixed responses/opinions.
i don't think there's enough empirical data available to support or deny that mixing battery types and capacities and specs causes any major problems. There's some anecdotal info, depending on who you ask.

Battery chemistry and physics are finite measurable sciences. Surely somebody, somewhere, has asked the questions of enough qualified engineers and scientists to come up with a definitive answer? I can't believe there is still such a wide variance of opinions presented as answers on something that should have been set in stone a long time ago. I haven't heard of any specific scientific research on the subject that supports or refutes it either. I have seen lots of expert opinions passed off as fact, that invariably differ from the next one I read.
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