Loosing coolant rapidly

I wondered how long it would be before asking a question on here. 100 miles it turns out!

Brought my 1985 3.5 RRC a week ago. Checked coolant on purchase and seemed fine.
Just before I took my car for its first drive yesterday i re-checked oil and water and found no coolant in header tank. i filled it and there was a little bubbling but i guessed it was just because it was so low it took some air around the pipes.

After about 35 miles of driving i re-checked the coolant and found it at the bottom of the header tank. I topped it up and just put it down to the coolant settling again.
Drove into work (about 15 miles) and re-checked the coolant and its just visible at the bottom of the header tank.

Uh oh!
Thinking the worst i but a dye test on it to check for head gasket and found it ok, no change in colour. Also had a very long hard look at all the pipes from above the engine and below and found no obvious signs. Put a pressure guage thingy on the header tank and blew up to 15psi and found pressure to be dropping, about 1 psi in the first 10 seconds. Expecting to find it pushing out coolant somewhere i had another look and couldn't find anything repeat blowing up and looking 3 times.

No wet carpets, no obvious leaks, no white smoke from exhaust and no change in colour on a dye test. The car starts fine and seems to go alright, I have run out of ideas!

I have done a bit of digging about and couldnt find anything. Does anyone have any suggestions?

It's leaking from somewhere believe me. New antifreeze has a habit of finding leaks where none existed before. Keep looking.

Header tank cap faulty? Run it up to temp and see if it's coming out the overflow. Valley gaskets used to be common on them as well for mysterious water loss.

Could try a leak sealer? just to see if it stops it. Other places, Heater, Radiator, and on Classics sometimes the header tank splits, looses the coolant and closes up again. I think I have a couple (one is split and gave same symptoms) you are welcome to both, no cost just post, if you find its the header.

strangely i got given a spare rad+ header tank when i brought the car. Previous owner said it got given to him so was just passing it on but thanks anyway stopover

Not comming out of the overflow. I left the pressure dial on the header tank and ran it up and didnt seem to go anywhere near the header tank rating. It doesnt seem to pressurise up enough.

I could try a sealing product but i didnt really want to as i worry about a sealing compound going into all the little holes of the heater matrix and clogging up. I am sure thats what made my heater marix explode in my last car.

I shall try with a stronger concentration of antifreeze and see if i can find a bright blue mark somwhere. I suppose the oil leaks could be making my life a little harder

What/ where is this valley gasket? i assume its in the middle of the V but what does it do?

The valley gasket is one big gasket that forms the inlet manifold gasket and covers the cam/tappets up. If that's leaking you should be able to see coolant coming down the bell housing. It may well be the radiator though as it's impossible to see all of that.

I shall do some more probing in the daylight

Have a very good look at the core plugs. There are two you can't see on the back of the block so have a check for signs of coolant around the back typically at the bottom of the bell housing.

Another odd leak is split hose on the plenum, normally the split will be at the bottom and at idle you won't see it but get an assistant to rev the engine and it will become obvious but I guess yours is on carbs so will be a different set up but do have a careful look and check on all coolant hoses including the ones to the heater where they dive behind the engine.

HTH

spent an hour or so looking today. No leaks to be found on idle or whilst revving. Removed fan surround and grill to look for rad leaks and found none. Found someone had fitted twin electric fans in front of the rad, removed fuse and tried to get hotter to pressurise the system a bit more. Still no leaks found. Replaced all removed parts and fuses and took her out for another drive today. Checked header tank at destination and found it to be pressurised up with some gurgeling and overflowing. At this point i noticed the rad seems to be higher than the header tank so removed bung on top of rad and filled up with hot water from there.

On returning home i squeezed hoses and found them to be rock hard. :violent: Sounds like headgasket but i don't understand how i wouldn't of seen this before. Unless there is another way of pressurising the system? The gauge sat in its normal 1/3 of the way up but would there be a possible for it to happen somehow else? I am hoping that maybe there was an air lock and it was just expanding and blowing the coolant out but i dont think i can be that lucky.

The rad doesnt look that brilliant. Would it be possible that it would restrict the flow of water, then the water gets too hot and boils and the steam pushes out the water?

You say you got another radiator with the car? Have you tried that one?
If you can get hold of a block tester (do a Google - Block Tester) this will tell you if it's a head gasket. Solid top hose is a sign of a head gasket gone. Twin fans on the front is normal if you have air/con but someone might have put them on to help cooling.
Had a Volvo Estate that had a rad leak that you could only see at night with a torch to show up a very fine spray of steam coming out of the top of the rad. Also a large cardboard box unfolded and placed under the car shows up leaks better. As mentioned Core Plugs are a possibility. Have you done a compression test, taken the spark plugs out to see if any difference in colour or showing water. Oh and the black header tank I mentioned before split down the seam (hard to see) not the top.

I did have a look at the header tank but couldnt see anything. I shall try the trick with the cardboard but i think the damage has been done now. I shall see if i can find a block tester tomorrow and check again. I have already checked and there was no colour change but now there is so much pressure in the system i am convinced its head gasket

Havent taken the plugs out yet as i didnt have any tools with me. Another job for tomorrow. What will the difference in colour be?