I have a very, very slow leak in my cooling system. Today I discovered a crusty, salty, whitish buildup around the expansion tank cap. I assume this means the cap should be replaced?

In your folks experience is it ever necessary to replace the expansion tank and the small hose that runs out of the top of the tank? I'm considering replacing those 2 items and perhaps the upper radiator hose all at the same time.

BTW - I replaced my radiator and the lower rad hose in March.

Thx,
J

If the cap is 16 years old, replace it. The bottles seldom crack. The small hose is cheap but it probably doesn't leak either.

I wonder why you didn't replace the top hose when you replaced the bottom. If you replace it, get new clamps. Also measure the distance from the radiator to the clamp and make sure the new clamp is the same distance - the plastic tube from the radiator does not like to have clamp spots. AND, do not over tighten the clamps at the radiator end.

Have you checked the heater core for leaks? Or the water pump gasket?

Klaus
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Did you do your Random Act of Kindness today?

Cap looked good. No visible cracks.

I didn't replace the upper hose because it looked fine. Did replace the clamps. I might replace the upper hose and cap just for peace of mind since I don't know how old thay are...

Where is the best place to look for water pump gasket leaks?

What's the easiest way to access the heater core to check that.

Thanks for any help!

Water pump is just above the crank, you need to remove the timing belt cover and look for greenish staining.

The heater core us to the right of the gas pedal, just remove the cover under the dash and have a look see.

Klaus
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Did you do your Random Act of Kindness today?

Great, many thanks!

Jim

It is not necessary to change the expansion tank simply as maintenance.

Unless it is cracked beyond repair and cannot hold pressure.
The white crud is probably calcium buildup. Try to clean it before just buying something new. It's not entirely unusual to have calcium build up in the cooling system. Obviously it would be better without it though.

I would replace the hoses if they are leaking, but if they're not, that is not the source of your missing coolant.

Finding a coolant leak can be tough. The small ones usually dry up before you can find them...

Cap looks okay. Any other locations to check?

How do you define "very, very slow leak"?
How much over how much time are you losing?

The tank level has dropped maybe 1/4 to 1/2 inch since I put in the new radiator in March.

Could it be normal evaporation that would occur in hot weather driving? Maybe I am being a little too anal about this??

The cap and top of the tank look fine. I'm going to clean the bottom of the tank and keep an eye on it and the hoses for any sign of leaks. I'll also check the heater core and water pump as suggested by Klaus.

Have you been topping it up and noting a drop?
Or just the drop since the radiator change?

Personally, I wouldn't sweat a 3/8" drop in the expansion tank since the radiator change. I wouldn't even think of a leak with that loss, but that's just me.

Even ambient temperature can affect a reading - although very little.
Yes, there will be some evaporation, but I have no idea how much. After all, the expansion tank does have some facility to vent under excess pressure.

Mark the level with a grease pencil and watch it for another month. Always use cold engine readings. Some of your 'loss' could have been air bubbles from the radiator swap, if the level does not go down any more.

Klaus
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Did you do your Random Act of Kindness today?

Okay, it's now been about a month and a half. There's is no further coolant loss. It must have been due to the radiator replacement...:)

I think the cap might also have been too loose. Cleaned the cap and tank, retightened and the calcium deposits have disappeared too.

I have found cracks at the base of the threads, where the threaded portion mets the tank.

Checked cap, no visible cracks.

Actually, I was not referring to the cap, I was referring to the reservoir.

Where the threaded portion on-which the cap fits meets the rest of the reservoir, I have seen several instances of cracking.

Okay, I'll check that after my car cools down...:)

Thanks!