Radiator issues and electrolysis


I wanted to pick you guy’s brains about a radiator issue I’ve been having with my truck. Bear with me- trying to be detailed as possible here.

Bought my '91 Ranger in '99 about 105K miles ago. The original radiator began leaking in colder weather during warmup. A radiator shop attributed it to normal wear. No problem- bought a new Modine single core radiator- same size as the original. It was relatively inexpensive, but had a lifetime warranty.

Two years later, upon startup on colder mornings, this radiator begins to leak again. It appeared to be leaking between the aluminum core, and plastic reservoir. Probably a fluke I figured, so it was replaced under warranty.

Fast forward another two years, and the same leak happens again in nearly the same place. A repair shop actually informed me of the leak between the core and plastic tanks when I had the truck in for service. By that point, I attributed it to poor quality on Modine’s behalf and opted for a larger, double-core radiator specifically made for my truck by Northern, a different brand than Modine. It was a stock, OEM-certified product. Now I didn’t opt for the double-core due to overheating problems as I have never seen the engine come close to overheating. Rather it was about the same price as the single-core radiator while automatically gaining additional cooling capacity- win win I thought.

This new Northern radiator came with a one year warranty, and I installed it two years ago. Well, about eight months ago just after the warranty expired, I noticed a little coolant seeping from the very top tube of the radiator near the cap- where the cooling fins appear to be soldered/welded to the tube. And no, the radiator cap is not leaking- I’ve checked many times.

The leak is still very small, but now that I am about to make the two year coolant change, I am thinking about yet again replacing the radiator. I’ve read up on electrolysis, and thought perhaps this could be the problem. Broke out the volt meter, followed the procedure of connecting the negative lead to the negative battery terminal, and sticking the positive lead only in the coolant of the radiator. With the engine off, the meter read -.02 to -.12 volts. During startup it spiked to +.55 volts, and during idle, it fluctuated between -.08 to -.25 volts DC. Apparently, +.3 volts is acceptable, but I’m concerned about the spike during startup. The battery cables are relatively new, but do need to be cleaned at the battery.

I’m stumped on this. Could this be just dumb luck? I’m not positive the first two radiators failed due to electrolysis, but could this have been the case this time around? I can’t imagine it being normal to average a new radiator every two years, but perhaps I’ve been getting ones that have been overlooked by quality control!

Any input and experience with this is appreciated. I do a fair amount of work on this vehicle, and have decent knowledge of basic electrical work.

Thanks a ton in advance- I know there are some great auto gurus on this board!


dusty i read your post, then thinking i had nothing to add, left it. but after thinking about it, i thought TWO years between every radiator sounds funny. think back what else are you doing every two years on a maintenance basis. is it possible you are using that particular area of the radiator/ housing area as a resting place for tools, prys, or leaning on while you do your other regular maintenance???


Good question. No, it appeared that the first two radiators began leaking from the lower, passenger side seam where the lower radiator hose attached, and attaching them didn’t require any great amount of force.

Now, regarding the current radiator- the leak IS at the top, but the cooling fins are covered on top by an aluminum plate. Not sure if this picture loads, but if it works, you can see where the radiator is leaking. There is a little opening at the top where the fins look damaged, but that happened after the fact. I suppose it is possible that the fins were not properly welded onto the tubes, causing a weak spot- that’s what I am hoping is the case. Other than that, I do not put tools on top of the radiator, and it is hard to reach the cooling fins as they are.



It has appeared that most non-catastrophic radiator failures were the result of the flexing due to expanding and contracting in normal operation. Leaking head gaskets, incorrect radiator caps, and “flex” hoses can hasten these failures, as will electrolisis.


A couple of questions. What type of antifreeze do you use, not brand but color, green, orange, yellow? What concentration? Do you use any flush chemicals?

Failure of the rubber seal is fairly common, though not usually in two years. You can expect those to fail every 8 to 10 years or so. This last leak looks like dissimilar metal corrosion and it could be due to an inconsistency in the alloy or a copper line was touching the core in this area. I say copper because of the green discoloration. It could be coming from the brace on the side or the solder used to solder the fins on.


Very good post Dusty T. and I think you may be on to the cause of the trouble.

To see if you can lower the voltage in the coolant you could try to improve the grounding system performance. As a test, connect a jumper cable between the negative battery post and the engine block near the exsisting main ground lead, see if that cuts the voltage down significantly. If it does then you may need to replace the main ground lead. Also check and clean the other grounds that tie to the engine and frame from the battery. Check the voltage again after you do those things.

Wires can look good on the outside but be damaged internally with corrosion, as you probably know already.

Another thing that may cause this trouble is over pressure from a bad headgasket but I think your thought is really the cause though. If it was a headgasket you would have other symtoms also.

Keep us posted on your progress using this same thread.


Time at high voltage could be a problem. But you don’t spend much time at 0.55 volts since it’s only during start-up. I wouldn’t be too concerned about electrolysis.



I have been running a 50/50 mixture of green Sierra propylene glycol distilled water. I change it about every two years and install a new t-stat. Prior to that in the other radiators I just used the regular Prestone stuff. I do not and have not used any flush chemicals, just drain and refill. I did flush the engine via tap water 7 or so years ago shortly after I bought the truck.

Regarding the pic- the green is actually antifreeze. The brown, copper color appears to be dirt and wipes off, leaving it the regular aluminum color. I know, it looks like dissimilar metals, but I’m pretty sure it’s just dirt/dust.


Great idea on the jumper cable. I may give that a try. The battery wires and connectors are actually only about 2 years old, and I had replaced them myself with new OEM ones. This was actually a harness that connects the negative to a frame rail, and engine block, and positive to the starter motor. In hindsight, the battery terminals do need some cleaning, so I may just go ahead and do that, and see what happens. I’ll also check up on the ground strap and maybe see about getting a new one.

I should probably confess to a few more details here- I do have a 200-watt amp, driving lights, and an auxiliary battery in this truck- all of which I wired up myself. None are directly grounded to the radiator from what I can tell, and turning on and off these items with the engine on or off didn’t seem to make any difference in volt readings either, but I can check that again to be sure.

Thanks and I’ll keep you all posted.


Cougar and All-

To update, I went ahead and cleaned both battery terminals, and it did make a bit of a difference. It occured to me it has been more than a year since cleaning them, and they were well overdue.

After they were cleaned, I checked the volt meter again. with the engine off and accessories off, it read around -.04 to -.08V DC. Engine running, and all accessories, stereo, aux battery, fan, lights, everything, it fluctuated from -.14 to -.08V DC. Down from the .26 - .28V DC I was getting earlier. I didn’t see any major jump when turning on a certain item, except maybe the stereo, but that was about a .03V difference.

I did not check it this time while starting the engine. I may go ahead and do this later when I have some assistance and keep you all posted.

Otherwise, it seems to me that these numbers are okay- especially now. What you you think? While reading up on this earlier, I’m surprised no tech articles recommended cleaning the batt terminals, but it is certainly part of the grounding system…

Oh, and the engine was cold when I did this but I reved it a bit with the radiator cap off while checking the voltage and warming it up a bit.


Well I think you made some good change there. If there was a problem with it I don’t think it will be now, looking at the new readings.

Thanks for the update.


Okay, I went ahead and checked the voltage during startup. The meter spiked up to .25 volts w/ starter engaged. I don’t even think it reached .3 volts. That’s way down from the .6 volts I was getting before cleaning the battery terminals. So I suppose let this be a lesson to clean the batt terminals more often. I think I am going to chalk these radiator issues more toward poor quality, since I’m certain the leak began much sooner after I had maintained the batt connections. Unless someone wishes to disagree, I conclude that electrolysis is most likely not the issue here.

Thank you for the help and any future suggestions!


Well, I think then you may have just had some bad luck. I’ve used the Sierra antifreeze in the past, I don’t think it causes any problems. I left it in one car for five years and it didn’t hurt anything, but I wouldn’t do that again. I hope they come out with a HOAT formula so that they can stay competitive. There is a HOAT Propylene Glycol formula on the market and the manufacturer claims it will last for 7 years.


Just one more wire. The one that connects the engine to the frame/firewall/fender, wherever it may be. See what happens when a jumper cable connects engine to frame/firewall/fender. Any one of the three should do.



Some clarification needed- should I do this still, despite the low numbers I am now getting after cleaning the batt terminals? Or, is this in response to my original post?

Either way, I can certainly run a makeshift jumper between the engine and frame rail ground if need be.



i purchaced a radiator cap for one of my cars that continuesly has rusty deposits that cured the problem the cap has a zinc anode on a spring that hangs in the water passage and the rusty deposits have gone down to a minimun since doing this
i also found a loose ground that went to the a/c compressor knowing that loose wires sometimes can cause electrons to take diffrent paths where ever the resistance is less
i re wired the ground on the compressor strait to the negitive on the battery and removed the zinc anode radcap after a couple weeks i checked the water and it was still rust free noticing this i ran the a/c more than usaly to see if this was really the problem once again the rust apeared in the system after about 2 months. frustrated with this i started to check for other things that could be introducing some extra
electrons in the system i only found one and it happened to be a spark plug wire that had rubed a spot in the insulation just enough to send a lil spark (found it in the dark) right on the suction line of the a/c so i replaced the wire and flushed the rust out once more and now the antifreeze has been free of rust for 4 months and no sign of it since then i have noticed that the engine runs cooler by 5-10 deg. in stoped traffic im not sure if the electrolisis was causing the engine to run hotter but i have my suspisions that it may have been the combo of all of it.

I took my truck to Jiffy Lube for an oil change i figured that they had been around for years and knew what they were doing and from the waiting room i watched them take a garden hose over to another car and fill up the radiator with tap water. i had took my girlfriends “pink” 1999 chevy 4x4 truck there about a year ago and had a radiator flush done to it so i put two and two togeather went to her house checked her water it was full of rust too! gritting my teeth i took it back to jiffy lube and told them i think its rusty due to them they didnt think it was thair fault but they flushed it out once more for free this time but they had it hooked up to a machine this time and the last time they didnt use it they drained it into a pan and used 1 gallon antifreeze jugs to fill it i bet they toped it off with tap water too i wasnt watching them as close as i shoud have but i think thats what made it get all rusty.
9 months has gone by now and my girlfriends truck sprouted a leak at the rop of the tank by the hose connection we took it to the dealer to have them fix it they told us this was due to someone adding two types of antifreeze and neglect the radator was all sluged up and needs to be replaced. none of this is too bad to me but driving a PINK jacked up 4x4 without tented windows around town to get it fixed is killin me