After a recent possible overheat (hose blew off, warning light came on and I pulled over) my car is using coolant. 20 miles drops the level of the tank about a inch.

I have a kit car with a Rover 3.9l V8. I bought the short block off a guy from eBay as a 'new' reconditioned block that V8 developments had pressure checked, a balanced crank, new shells, rebored with new pocketed pistons. Supposedly it had top hat liners in as well but they didn't look like top hats to me. (knowing nothing about engines at the time I took his word) I have no paper evidence this was all done but the block certainly looked new, the pistons were pocketed and the bores newly honed with zero evidence of wear. And the crank had evidence of balancing. The cooling system has a radiator from a TX1 black cab with a non-pressure relief cap on. The header tank is a VW globe type.

There is no evidence of pressure in the system. The pipes are still easily squeezable when warm. 30 minutes after the engine has stopped you can open the header tank with a gentle hiss of air. No sign of oil in the water or water in the oil. When cold starting there is not very much smoke from the exhaust, if I blip the throttle a normal amount of smoke comes from the exhausts.

The car heats up as normal and drives as normal. When sitting in traffic the fan kicks in pretty swiftly but the temp gauge drops when the fan kicks in. No more overheats.

I can't find any leaks anywhere, I did 35 miles last night and put about half a litre of water in afterwards. Got a torch out a searched for leaks but I can't find any.

The only evidence I have to where the water is going is on first filing the water system up and rebleeding, the system chucked water out past the seals of the rad cap. I assumed I had overfilled the system and the pressure found the weakest point (why the pressure relief on the header tank didn't go first I don't know), or I hadn't screwed it down correctly. This hasn't happened again.

I am struggling to believe the water is leaking and I am not finding a leak. This points to a blown head gasket (tin) or a dreaded dropped liner. But I have no evidence of either other than coolant loss.

Any thoughts?

There are three modes of initial head gasket failure
(1) Directly into the cylinder past the fire rings.
(2) Into the oil drain galleries
(3) External.

The first 2 types can usually be confirmed by testing the air in the coolant tank for traces exhaust gas either chemically or by using an MOT style gas tester.
You could also try a cylinder leak down test but this rarely shows anything unless the gasket is already on its last legs.
The only viable test for the 3rd type of failure is a cold pressure test on the cooling system.

[Edited on 10/6/16 by britishtrident]

air lock? Check this on mine by pressurizing the coolant with a hand pump (engine cold not running) to 1bar (pressure cap opening pressure) and observe the fluid level. Found mine would decrease, i.e. air/gas locked. Once air is out the level will not change as you pressurize the coolant system cold...

Dan

I run my header tank about a third full, as it gets hot it rises to about 3/4 at a guess, as it cools it drops. I read somewhere that the bigger the engine the bigger this change is.


when i ran it higher in the header tank, it would blast past the cap.

could this be your scenario?

(mine is an ali tank and I can't see in it, so I am guessing on the rise height based on what it settles to)


I thought I had raised a post on here about this, but I can't find one.

Do rv8's need a header tank? Or will an expansion tank from the rad cap do???

There is a little water bubble off 1/4" pipe by the thermostat, it's the highest point of the inlet manifold, this can get blocked and the car will exhibit what you are experiencing, it should run directly into an expansion tank or top of the radiator. If it gets blocked then bubbles created when the water boils in the head do not have an easy escape so create an air pocket and the car starts to overheat and blow water out the expansion tank cap.

Also before worrying about the head there are 2 bolts that go into the water jacket that hold the inlet manifold on at opposite corners, these need to be sealed with a smear of blue hylomar or similar before being bolted up or the water will weep past them and evaporate off.

Agree with several of the suggestions sniff test with a gas anyliser and blockage in the breather pipe. It's possible a pressure test may show up any leaks
but if that fails I've found that using an U/V dye and lamp very useful locating hard to find leaks . Ring Automotive supply small bottles of dye

When I had the TR7 I had this issue. Over one winter I pulled the heads & had them skimmed 1mm to get the CR up. (it was a defender lump @ 8.3:1) Afterwards it never used coolant so it looked like an issue under higher revs where the gasket leaked. Was fine driven gently or at idle.