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SOLVED (mostly)
Changing out the middle hose, as was recommended, stopped it from losing 8oz per week; although it's back to it's normal behavior of losing 2oz. per week. For more fun see my latest mystery problem post. https://www.yotatech.com/forums/f116.../#post52503650
Hi... For the past few years (four - five?) my '87 pickup (22R) has been losing about 2oz. of coolant per week despite me replacing every radiator and heater hose under the hood. Looking under the truck there was never any sign of a leak on the driveway. But, these past two weeks it has begun to lose 8oz. per week and leaving evidence of the leak on my driveway under the truck. I checked the clamps they were tight and there was no sign of coolant on any of them. From under the truck I can see that the coolant is making it's way down from somewhere and it's dripping off of the bottom of the alternator. Using a flashlight, and looking from under the hood and under the truck, I cannot for the life of me see where that coolant leak is originating. I'm asking for suggestions for where to start looking before I start removing parts. Thanks.
Last edited by Den.; Jan 24, 2026 at 05:17 PM.
Reason: solved the problem (mostly)
Borrow or rent a cooling system pressurizing tool from one of the large auto part retailers and see if pressurizing the system cold might reveal the source of problem.
You could do a pressure test like recommended above, but if you can't seem to find it that way and it's some sort of weird intermittent loss, you can also use some of that UV dye and a uv flashlight (they make kits for about $10-15 on amazon) which can be pretty great at tracking down random leaks when it's already dried up. I used that on one of my cars when I was having a leak I just could not find and was super intermittent and found it that way. Worked pretty well.
"Dripping from bottom of alternator" -- yep. Mine did that. Leak was from the hose-to-pipe connection above the alternator. It'll eventually trash your alternator. Replace that hose, and be ready to spend some quality time removing the corrosion on the pipe before you install the new hose. See how mine developed a slit failure? Also, there was a lot of corrosion inside the hose.
If you look in your engine bay you'll get that answer. I don't recall and I'd have to take a look to refresh my memory of it.
I think it was this hose: engine-to-pipe lower radiator hose #16573-38020, AKA #1657338020, HOSE, RADIATOR, NO. 3; RADIATOR, OUTLET
You can look up the part on-line to see diagrams of where it goes
If you look in your engine bay you'll get that answer. I don't recall and I'd have to take a look to refresh my memory of it.
I think it was this hose: engine-to-pipe lower radiator hose #16573-38020, AKA #1657338020, HOSE, RADIATOR, NO. 3; RADIATOR, OUTLET
Yup, I removed mine a while ago but if I remember correctly a lot was done from underneath, I didn’t have to replace my hose but I did have to replace my alternator which will not come out without removing at least one side to get the alternator in.
Last edited by Discombobulated; Dec 2, 2025 at 02:04 PM.
Yup, I removed mine a while ago but if I remember correctly a lot was done from underneath, I didn’t have to replace my hose but I did have to replace my alternator which will not come out without removing at least one side to get the alternator in.
I have swapped the alternator without removing this hose -- it's just a bit more difficult.
Nov 23, 2025 | 10:36 AM
