So I'm chasing an odd coolant leak in my B18/20 Frankenstein build. Block is an over-bored B18.

There is coolant slowly dripping from the bell-housing under the car. As the car sat all winter, the coolant drained enough to get below the level of the leak, so it "stopped".

At first I thought it was the coolant pipe and the 90 degree fitting on the rear of the head. Both were somewhat corroded and testing it showed that they had small leaks when the hose clamps were tightened down. Put in a brand new coolant pipe and a brand new 90 degree pipe...no leaks from there any more.

Filled up the system again, back of the head and top of the block and bell-housing are bone dry, but the coolant drip under the car started again.

Question: Is there a coolant plug of some kind at the rear of these blocks? The only freeze plug I remember seeing was the one over the back end of the cam. But I think I remember seeing a small npt plug back there, and am wondering if that's leaking. If not, then is it possible I have a crack in the block that is allowing the coolant to drip out by the flywheel (which would utterly suck)?

I plan on pulling the trans and flywheel once the weather gets consistently better, but I'm a bit vexed as to what could be causing this.
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Tony - 1958 Volvo PV444, 2012 Volvo XC70 T6 Polestar

Perhaps a quicker attempt to resolve the leak may be to check the torque of the head? It's a shot in the dark and would only take 15 minutes.

I already re-torqued the head after the first time it ran. And am hesitant to do it again. Also, to repeat, it is NOT leaking from the head, as the entire engine block is bone dry between the head and the bell-housing or oil pan.

To answer the other question, it does it when it's not running, so it's not a pressure-related leak. Matter of fact, it may stop when the engine is running and warmed up...I have to confirm that.

I am leaning towards a crack in the rear of the block. I'm going to pick up a cheap scope from harbor freight, remove the inspection plate behind the oil pan, and see if I can view the source before I pull the trans and flywheel.

I appreciate all the suggestions.
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Tony - 1958 Volvo PV444, 2012 Volvo XC70 T6 Polestar

The point of a pressure test is to force the leak to get worse so the source is easier to spot. -- Dave

Are you checking for the leak with the motor running/not running? Have you tried to pressurize the system. I think I recall my old Stant cooling system pressure pump will fit right on to the radiator of a 544 or 122 - unlike 140/240 systems that require a simple adapter for the over flow tube. -- Dave

How big is the bore? B20 head gasket to go with the B20 head?

There is nothing behind the flywheel that leaks water, If you are 100% sure heater pipes and hoses are not leaking, then it could be the headgasket, or something like the waterpump O-rings leaking and the water running from the front to the back along the outside edge of the head gasket.

If the Welch plugs are factory, don't go pulling them out unless you are sure. The original cad plated steel ones are unbeatable.

The block is bored out to B20 spec, I'm using a B20F head, and the head gasket from a B20. It all lines up just fine. I made sure of that before I put it back together.

Few things to clarify:

The leak is manifesting itself from the bottom of the bell-housing, where the inspection cover meets it. It can't be the heater core because the leak is not in that area.

The coolant pipe along the side of the block is brand new as are all the rubber hoses. A leak at the o-ring by the water pump would not travel up that pipe, as that is something that occurred with the old pipe and it drips straight down from that o-ring/water pump.

The 90 degree elbow at the back of the head is also brand new.

The heater valve is bypassed right now, so hoses only run to and from the heater core. All of those hoses are dry, as are the hose fittings at the back of the head. The top of the bell-housing, the back of the head, and the top of the engine block back there are all bone dry. In fact, I haven't even run the car since I refilled the coolant and it started leaking.
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Tony - 1958 Volvo PV444, 2012 Volvo XC70 T6 Polestar

The o-rings on top of the pump can let coolant travel around the left side of the block and then run down the block and through the bellhousing.

If it only leaks while running, I think I'd just drive it with a loose cap until it leaks properly!



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An alternative falsehood is an alternative fact in a post truth world. - TG.

It leaks when it's not running, Paul.

Even if the O-ring from the water pump was leaking the way you mentioned, the top of the block where it meets the bell-housing would be wet. Again, that area is completely dry, as are both sides of the engine block where it meets the bell-housing.

I'll give everything a check between the water pump and the bell-housing, but I'll admit I'm skeptical of that being the cause.
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Tony - 1958 Volvo PV444, 2012 Volvo XC70 T6 Polestar

Thankfully, Volvo did not put any coolant passages in the back of the B18 or B20 blocks and I am pretty sure the B30 and the B21/B23/B230F don't have them there either.

That plug you saw is for the oil galley.

There is a 45mm core plug at the back of the cylinder head and if the leak is back far enough it could be coming from the heater box drain hose.

If the leak is from the rear cylinder head core plug, you will have to pull the head to change it.

If the coolant is coming from the heater box it could be the heater core, but check the heater hose clamps and heater hoses 1st.

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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com