Heaters going cold at idle

[daz_vrs]

Ok guys so I'm having a bit of bother with the vrs. Quick back story, cars had in the last 1k miles, head rebuild Inc head skim, new head gasket and pd150 head bolts. New radiator

 

Last week I noticed a small pool of coolant under the car when I drove off the drive and upon inspection it was coming out of the overflow in the expansion tank. Everything under that area was soaked in coolant. I took it back to the garage where the work was done and it was suggested to run without the thermostat to eliminate problems there but couldn't get it booked in for a week. 

 

So once I got the car back home I left it running on the drive with the expansion cap off to warm up and see what was happening. I found very poor flow coming back through the return pipe to the expansion tank at idle. It would spit a bit and then completely stop for a few seconds and repeat. Also the pipe coming from the thermostat remained cold when the engine was up to 90degrees on the dash and 98 degrees reading the ecu. 

 

So I changed the thermostat thinking it to be stuck closed causing poor coolant flow. This changed nothing. Even tested the old stat with boiling water and it opened as it should. So with this and still hardly any flow I thought water pump was failing so had this changed for a new one and no difference. Inspection of old pump showed no problems. 

 

As it stands at the minute on idle temp gets upto 90 on dash but rises into the 100s with blowers cold and radiator cold. If I rev it the heaters get hot and the temp drops. If I keep the car revved creating better flow eventually the rad gets hot and the fans kick in (98 degrees ecu reading) but I'm certain the rad is getting hot through the top hose eventually getting to the bottom hose so back to front. I'm not sure the thermostat is opening. 

 

If I leave the car to idle blowers go cold again. If I drive the car around the block the rad goes cold. Could I have a blockage somewhere? Should I be worried the new head gasket has failed? 

[Breezy_Pete]

17 minutes ago, daz_vrs said:

I'm certain the rad is getting hot through the top hose eventually getting to the bottom hose so back to front

 

Pretty sure that's the normal direction.

 

18 minutes ago, daz_vrs said:

Should I be worried the new head gasket has failed? 

 

Check for residual pressure in the expansion tank when the car is stone cold.

[daz_vrs]

3 minutes ago, Wino said:

 

Pretty sure that's the normal direction.

 

 

Check for residual pressure in the expansion tank when the car is stone cold.

I'm probably mixed up here. The hose coming from the thermostat should get hot when the thermostat opens and then the heat travel in that direction? Because what I have is the bottom hose getting hot from the opposite direction. 

 

I'll check for pressure once the cars cooled down completely

[Breezy_Pete]

Flow through radiators is top to bottom, flow through engine blocks from water pumps is bottom to top.  As far as I understand.

[KenONeill]

@daz_vrs - My understanding of the water circuit flow is as @Wino says, going right back to the days of non-pressurised thermo-siphon systems.

 

As to "remove the thermostat", wouldn't it be quicker and easier to feel if the top hose is hot when the gauge is up to 90C?

[daz_vrs]

What's people's thoughts on the poor coolant flow? Heaters only getting hot when the car is revved? 

[sepulchrave]

Gas bubble in the heater matrix from a leaky head gasket. Heater matrix is the highest point in the system so any gas collects in there. Revving it blows the bubble back into the system.

[Breezy_Pete]

1 hour ago, sepulchrave said:

Heater matrix is the highest point in the system

 

Are you sure?

The red ring is around the heater matrix pipes, the matrix itself sits horizontally just the other side of the bulkhead.

Is the expansion tank perhaps a tad higher?

 

[sepulchrave]

Literalism is the enemy of comprehension.

 

The expansion tank already has its own gas bubble.

[Breezy_Pete]

Half the engine is above the matrix, 'dude'.

[sepulchrave]

Look, the garage hasn't done the job right.

 

It's airlocking and the system is over-pressurising, hence the coolant from the overflow, airlocking is caused by combustion gas in the cooling system, over-pressurisation is caused by combustion gas in the cooling system.

 

Get as hostile as you like but this issue is head gasket related.

[Breezy_Pete]

No hostility here, just facts. I already suggested checking for residual pressure.

[daz_vrs]

Well I spent a bit of time on the car last night making sure there were no blockages or air in the system. Got everything nice and hot with rad fans coming on at 95 degrees and blowers blowing hot ( although these would go cold throughout the bleeding process) coolant level spot on. 

 

Drove it to work this morning and blowers were getting hot, thought I'd cracked it. Then within a few miles heaters go stone cold. Parked up outside work and revved it for a bit but they remained cold. 

 

Now 3 hours later I decided to see if there is any excess pressure in the system as it has had time to cool down. Opened the expansion cap to be greated with a Lound hiss! I only drove 8 miles to work and the temp didn't even get to 90 by then. 

 

Looks like this head gasket change has failed. I've only done 1k miles 

[sepulchrave]

1 hour ago, daz_vrs said:

Well I spent a bit of time on the car last night making sure there were no blockages or air in the system. Got everything nice and hot with rad fans coming on at 95 degrees and blowers blowing hot ( although these would go cold throughout the bleeding process) coolant level spot on. 

 

Drove it to work this morning and blowers were getting hot, thought I'd cracked it. Then within a few miles heaters go stone cold. Parked up outside work and revved it for a bit but they remained cold. 

 

Now 3 hours later I decided to see if there is any excess pressure in the system as it has had time to cool down. Opened the expansion cap to be greated with a Lound hiss! I only drove 8 miles to work and the temp didn't even get to 90 by then. 

 

Looks like this head gasket change has failed. I've only done 1k miles 

 

I know, I'm sorry, it wasn't done right. I hate to say told you so but...

 

If you have a receipt then you have a warranty, the garage won't like it but it's the law.

[daz_vrs]

1 hour ago, sepulchrave said:

 

I know, I'm sorry, it wasn't done right. I hate to say told you so but...

 

If you have a receipt then you have a warranty, the garage won't like it but it's the law.

Yeah I've already had talks with the garage who have said if it's the gasket it will be done at no cost. He has had me trying every other possibility first but I think we both knew. Even yesterday when I was bleeding the system and keeping the revvs up looking at the coolant coming back to the overflow it was full off small bubbles and not clear coolant. 

 

It's definitely the gasket as I tried pushing it on my way home from work this morning and the temp shot up to 120 degrees and blowers stone cold. It dropped back to 90 within half a mile. 

 

No need to be sorry or feel you told me so, I never disputed what you were saying, just hoped it could be something else. 

[KenONeill]

@daz_vrs - OK, I'm pretty sure that's HGF now, and that I would not trust anyone who suggested "take the thermostat out" as a diagnostic.