Cliff Harris

For years I've had a very small coolant leak at the thermostat housing. A little puddle of coolant would gradually accumulate over time:



I have tried various kinds of thermostat housing gaskets and none of them stopped the leak. I thought maybe the housing was warped, but it sits flat on a piece of steel that I have. One time I thought I found the problem when I discovered that the coolant hose on the throttle body was loose.

When I fixed my recent blown head gasket I spent a lot of time massaging the thermostat housing area. I saw that there were some pits in the gasket surfaces so I smeared some RTV on them to help seal the area. The leak was still there and I thought coolant was getting from the head-intake manifold coolant passage to the bolt and coming up around the bolt (the Torx bolt at the bottom of the picture, partially hidden by the EGR solenoid vacuum lines). I very carefully sealed the bolt.

Earlier this week I got a low coolant light and found a puddle under the radiator area. I thought maybe a plastic tank had cracked (happened to me before). The coolant was directly under the radiator and nowhere else, so I ordered a new DeWitts radiator.

Today I was driving the car and checking for leaks. I found a geyser at the front thermostat housing bolt. I thought the gasket was leaking and allowing coolant to get to the bolt and then coming up around the bolt. I have a Fel-Pro PermaDry thermostat gasket, which is a kind of O-ring (silicone) with a plastic frame that limits how much the gasket can be squeezed. I had used RTV and the gasket was stuck pretty well. I redid everything, using a stock cardboard gasket and Aviation Permatex. I figured that would stop the leak for sure.

I filled the radiator while the engine was running to get it full of coolant. When I shut off the engine I heard a high pitched whistling sound, which seemed to be coming from the thermostat housing. I found a puddle of coolant in the same old place. Sucks!

I cleaned everything up and started the engine with the MAF coupler disconnected from the throttle body to see if I could find the leak. I did find some coolant oozing out near the front thermostat bolt, but it wasn't coming from the bolt. It was coming from the thermostat housing itself! It looks like I got a little too enthusiastic sometime in the past when I tightened it down:



So why was there a puddle under the radiator? I think the coolant was squirting out of the thermostat housing and spraying on the radiator, where it ran down and dripped out the bottom of the radiator housing. I'll be looking closely at the old radiator when the DeWitts gets here...

don hall

Cliff, was this a 'time & material' job, or a 'bid' job?

GQ-ROD

Same thing happened to me once on another car, i was too exuberant and didn't realize what an inch pound torque wrench was for and over tightened and cracked the housing..........oh and an upper intake manifold right around a temp sender, so yeah now i use a torque wrench for everything.

Not that it would help if the gasket is misaligned, but i feel your pain.

You can use a coolant dye and UV flashlight and UV glasses to pinpoint the leak.

MikeT 90 C4sixer

Now that is funny! Glad you found the culprit. Must have drove you nuts, since you had done a lot of work trying to fix it. I was going to say that coolant should NOT be coming up out of that Torx manifold bolt that you mention. Motor oil, yea i could see that. I had a puddle of coolant in same place, but i think it accumulated over winter just sitting there. I have all new gaskets as well. I will have to watch it closely.

solaris_vii

Ive got a spare thermostat housing. Just pay shipping and its yours. Pm if interested

dizwiz24

My elusive coolant leak was a leaking radiator plastic sidetank.

I tightened, replaced elbow fittings. To no avail

Never occurred to me the radiator itself could leak.

Replaced it with a cheap delphi unit and all is good

Cliff Harris

Thanks for the offer, but I already ordered a new one.

I can't believe how much things like this vary is price from vendor to vendor. I saw everything from around $15 to $40.