Hello. My car overheated and now I have a very bad coolant leak in my 1984 308 QV. It pours out onto the sidewalk almost as soon as I start the car. I replaced the oil and coolant, thermostat; I even replaced the radiator with an aluminum one. I did all the stuff you are supposed to do when a 308 overheats. I traced the coolant leak to the hose shown in the picture below. This is the small diameter rubber hose that connects the top of the radiator fil/overflow tank to something in the center of the top of the engine. I dont think this small diameter hose is bad. What is the other end of this hose connected to and how hard will it be to find a leak in this area of the engine. Will I need to remove the plenum? Any help would really be appreciated. Image Unavailable, Please Login
That hose goes to a fitting underneath the intake plenum. Although the hose may look fine where you can see it, it is prone to leak at the fitting where it is clamped due to the high heat under there. There are 2 large diameter (1 5/8") hoses under the plenum also mounted one above the other. You could also have a leak in one of them . The leaked coolant could wind up in roughly the same place. If one of these 3 hoses is leaking, I'd recommend replacing all three. As mentioned, that's a high heat area and those hoses are more apt to go before many others on the car. Good luck.
I forgot to reply to the rest of your question. To determine if the leak is coming from that area, stand on the passenger side of the car and feel around under the plenum . It is tight under there. If your hand can't fit , start the car up in the dark and look under there with a flashlight. You should be able to detect the leak that way. Replacing those hoses is a bit of a chore, but it can be done without removing the plenum. You remove the air box and may have to move another accessory ( I forgot the name of it) to get at the hoses. The large hoses are 40mm , but 1 5/8" fit just fine. (Many people recommend 1 1/2" but I couldn't get that size over the pipes in that area). I used NAPA Gold Stripe hose on my car--it's very good quality stuff. I believe that there is a detailed description of this job somewhere in the archives.
Aside from all the hoses, there are coolant manifolds under there also. The are bolted to the heads. By overheating, you could have blown out one of the gaskets on the coolant manifold. If it were me, I would remove the plenum and check it all out. I would first unbolt the throttle body from the plenum so you don't need to mess with the throttle cable connections. next, use a gear-wrench to remove the eight nuts holding the plenum to the intake riser. Dissconnect the few vac lines and leave the cold-start connected. Beware of the eight little spacers that are around each bolt. They are in the thick black rubber gaskets between the intake riser and the plenum. If they come free- they could fall down into the engine. Mine were no problem and stuck to the gaskets. By removing the plenum- working on these hoses and coolant manifolds becomes much simpler. It should take about 30-45 minute to remove the plenum. The gear-wrench makes it much easier to get to a few of the hard-to-reach nuts. Attached are photos of the back of the plenum with four of the eight spacers highlighted, and another of what it will look like when the plenum is removed. You can see part of the manifold in the second picture. If it needs to be removed, you will need to remove the intake risers. Also an easy task- except for removing the old gasket material after removal. Image Unavailable, Please Login Image Unavailable, Please Login
