Mystery Coolant Leak
 

I have a very slow leak that's more of annoyance than an actual problem yet. About once every two months, I have to add about a half-quart, or less, of coolant to bring it back up to the line (I only put a couple hundred miles a month on my truck). I know it's leaking externally and not a bad head gasket or anything internal since I can smell it occasionally when I get out my truck. I've given it a quick look over and don't see an obvious leak. My main question is where are the most common points for a leak to develop? If I know that maybe I can investigate those areas closer. Since I don’t have a signature yet, my truck is a late ’99 F350 V10 with 80,000 miles.

Welcome to the forum plenty of info and amusement to be had here.
This is from my old memory of past forum posts.
Have you looked in the engine valley under the intake manifold for moisture. There is a steel line which runs from the water pump to the back of the engine which, connects to one of the heater core hoses. I read once where this had corroded and was leaking.
There have also been at least 2 posts I have read where the intake manifold corroded thru at the thermostate housing. [This may be from never changing the coolant, who knows]
Pressure check the cooling system the leak should rear its ugly head.
Cheers :-partybud

That's exactly the kind of information I was hoping someone could provide. I'll have to search the forums some more too since I probably didn't search well enough before. I guess I'll have to take a look at the areas mentioned this weekend, I'm doubting external corrosion since I live in the desert, but since the truck didn't get driven much internal and external corrosion is a possibility.

I was trying to bump your post to keep it on top. Good luck
I think a pressure test would be the best method of finding the leak.
Coolant changes are often neglected although, the corrosion inhibitors in coolant have a finite life.

Since your truck is a CC you should have a vaccum operated heater control valve which basically shuts off the hot coolant from getting to the heater core when the A/C is ran. My sisters Explorer currently has coolant loss like you described and I traced it back to heater control valve leaking. The leak is small and causes coolant loss very slowly and it took me quite a while to find. I would check that out. (if you have one of course) My SC does not have a HCV however my dad's CC does.

Here is a link with pics. Post #7

how to replace heater control/bypass valve - Ford Explorer Ranger Enthusiasts "Serious Explorations"®

That's a good place to look, but as you said, that's if I have one. I don't believe I do. That’s probably why I have the typical problem with the early SDs where the air comes out slightly warm with the air conditioning off and the temperature all the way to the cold side and the A/C doesn't get as cold as it should. I'll probably do the mod next spring to add one though. I'm just glad my heater core isn't leaking; I had one leaking one time on an old VW Rabbit and it stunk and steamed up the windows.

UM, I have a 99 also and I had a similar problem.... It turns out I have a bad casting on my driver side head. Right where the intake portion of the thermostat housing meets the neck portion of the head, it took a while for it to really show up. One day i parked the truck and 20 minutes later I saw the coolant on the ground. It was a nearly microscopic pinhole. I am in the midst of pulling the intake now to have the head brazed on the truck. Good luck. Just one more thing to check.

Since the weather was nice today I spent about an hour trying to find the leak I posted about back in November. It is still a small leak, but I can definitely smell coolant when the engine is warm. I looked in the valley and don't see any moisture and I crawled under the truck looking for anything. I also don't see anything coming from the water pump.

Does anyone else have any ideas where this leak could be. Like I said, it's a very small leak and the smell actually gives it away more than the small amount of coolant I have to add once every couple of months. I have a similar problem on one of my cars, but I at least know where that leak is (I've just been procrastinating fixing it since I have to take the timing belt off that car to change the water pump). Also, although my truck is a '99, I only have around 80k miles on it.

Could it be your expansion tank cap might have a slight leak? I've heard these caps do go bad and cause a minor leak...although visible splashing on the belt tensioner.

Maybe that's where you smell it as well.

my leak is on the passenger side head. Right at front of head. Visible but slight. Not enough for me to worry about yet but..... probably just like on the driver side by thermostat housing. Maybe this will help you find it.

northwindone I have a similar problem. I'm losing 1/2 qt to 1 qt every 1000 miles are so. I never see any coolant on the ground or on the truck. I can always smell it so I know it's external. The other day I noticed that the smell was much stronger from the drivers side wheel well. I am beginning to think the gasket for the oil cooler is weeping. I had to pull the cooler when I did the headers so I could remove the dip stick end I broke off in the block. I'm going to check it when the weather warms up a bit.

Check your radiator for any staining. It could be high up, seeping slightly, and evaporate off before it ever hits the ground.

The other way to do this is with dye. Put it in the coolant, wait a few weeks and start checking with a black light. Even if the coolant evaporates, it leaves behind the dye which will show up like a spotlight.

I was just starting to think yesterday that maybe I should try some dye to find this leak. Wherever it's leaking, it's evaporating before it hits the ground, or even gets to somewhere I can see it for that matter. I'll give the radiator a good look over before I go with the dye first. Thanks for everyone's input and advice. I'll be sure to update this thread when I find the leak in the hope it will help someone else.

Coolant Leak Update
 

Well I finally took the truck on a camping trip over the past weekend for the first time. (Not all of our gear and the dogs would fit in the "new" T&C, darn! :-missingt) We went to one of our favorite campgrounds, and it is over 6,000 feet and the road goes from 3,000 to 6,000 feet in 5 miles and gets steeper and steeper as you as it climbs into the foothills of the very deep Owens Valley. The truck did great and we cruised all the way up the winding steep road at the 55 speed limit like I was just cruising down the highway, well other then downshifting of course. We've taken my old Nissan hardbody in years past and I was usually down to second gear doing 30 by the time we got to the campground entrance. The temperature gauge didn't even budge even though it was over 90 degrees at the bottom of the hill and I had the A/C on. I love this V-10! ...even if I did burn $150 of fuel over the weekend :'(.

Anyway, when we pulled into the campsite I could smell that annoying coolant smell again. I opened the hood and the coolant was exactly where it was when we left the house 200 miles earlier. I checked throughout the weekend as we had to drive off the mountain a few times for forgotten supplies, and even though I could smell coolant, the level never went down.

I guess the point of this post is to update that I still have no idea where the smell is coming from and to say that despite this annoyance I am very happy with this truck's performance. I just can't wait until I finally get a TT to tow into the mountains.

I think I found mine!
 

The fluid was leaking from the little hose going back to the expansion? tank. I bought a new radiator first though :-huh. Was told by two people, (mechanics) that it was for sure the radiator. Replaced the hose clamp and now no leak. I have now picked up a 28' TT and towed it up past truckee. What a great truck these v-10's are!!