Radiator story and pesky mud wasps

[Ace]

Thought I had a radiator leak: low coolant level in radiator, no coolant in overflow tank, wet coolant along the lower edge of the upper radiator tank, coolant pooled on gravel shield under engine. I had visions of hassle and expense of radiator repair or replacement.

To make a long story short, I discovered two things:

1) The coolant overflow tank vent was plugged by a mud wasp nest. The vent hose is a short rubber hose with 90° bend, not screened where it opens to atmosphere. The open end points down, so you don't readily see the opening.
2) The radiator cap lower seal appeared OK, but the upper seal was cracked. See image of radiator cap cutaway view:

Radiator cap cutaway-01b.jpg

So it appears that when the coolant heated up and tried to flow to the coolant overflow tank, it was impeded by the plugged overflow tank vent and leaked out from the cracked upper seal of radiator cap, then spread out along the lower edge of the radiator upper tank. I would have spotted this sooner if I had looked under the hood when the engine was hot. I more typically check under the hood before my infrequent driving, when the engine is cold.

My 1983 Tercel has the original radiator with plastic upper and lower tanks. Reading through some old threads about Tercel radiators, I'm wondering how long mine will last.

Mud wasps are a common nuisance in my area. These wasps favor holes of a certain size to make mud nests for their larva, like the ground pin hole of a regular 120vac outlet. Years ago I saw a situation where a little-used railroad freight car had air brakes stuck on, not releasing because a brake valve mechanism had an air vent plugged by a mud wasp. That shows how effectively they can plug a hole, even against substantial pressure.

Appropriate screening of air vent holes can prevent those problems.

[dlb]

Wow, that's some good sleuthing you did there, Ace. You just never know what weird causes you will come across for some problems. I will try to remember this for future reference.

Did you fasten some kind of bug screen over the end of that hose to prevent it from happening again?