Considerations related to H6 head gaskets and cooling system

Posts specific to the 3.0 litre NA H6 engine

Re: Considerations related to H6 head gaskets and cooling sy

Postby JezzaH6 » Wed Mar 10, 2021 7:10 pm

I've had to bleed mine a few times recently (playing around with radiator and thermostat setups) and agree with everything that BigBadBenny has added. Figured I'd add my $0.02 worth of experience!

I use a dedicated spill-proof funnel (can be bought cheap from ebay/amazon), but stuffing a funnel extension into another funnel is a great idea too. Make sure the heater is set to the highest temperature (32c) BEFORE draining the old coolant, and ensure its still set to that before filling the coolant loop again. Also ensure your radiator fans are plugged in and working.

Definitely worth putting the front of the car up as high as possible on jack stands. I also removed the coolant pipe from the top of the throttle body. Aside from the top of the funnel this is the highest part of the loop, and is connected directly to the lines that feed the heater core. This will help get the air out of the heater core.

Make sure you fill the system really really slowly! And I'm not talking about pretend slowly. Like glacial slowly. Aim to try and get about 1l per minute or less. Try and spend at least 6-8 minutes filling the system. This will give the trapped air a chance to get out. Make sure you don't let the coolant completely cover the hole in the bottom of the funnel- you should be pouring slowly enough that the funnel never actually fills, leaving a gap past the flowing coolant to give the least possible restriction for the air to escape.

Fill very slowly until coolant starts to spill out of the upper throttle body coolant pipe (after about 5l is added). Connect the upper pipe and its hose clamp, then slowly continue to fill the coolant until the funnel is about 1/2 full- this will give a bit of pressure to help force out bubbles in the next step.

With the car still on jack stands, make sure the car is in neutral, and start the engine. Let it run for a few seconds (less than 5), then shut it off. This will spin the water pump to help get any bubbles stuck in it and behind the thermostat. Don't let the engine run for too long though as this will force bubbles into the rest of the loop. You just want to dislodge them from the water pump and thermostat area. After turning the engine off squeeze the lower radiator and upper hoses to help get those dislodged bubbles out.

Do this a few times until you don't get any larger bubbles out when squeezing the bottom hose. Leave at least 30 seconds to 1 minute between doing this, both to ensure you don't melt your starter and to give the newly freed bubbles time to get out, rather than forcing them through the system when you start the car. For me this took about 3-4 turn on, wait 5 seconds, turn off, squeeze hose cycles.

After you're satisfied that you aren't going to get any more large bubbles out (and that your starter isn't going to melt :lol: ), start the car and let it warm up. Every now and then give the upper and lower radiator hoses a few squeezes to help move any smaller bubbles that may be trapped. Keep a tab on your coolant temperatures- ideally use torque or BTSSM to get an actual temperature readout rather than just relying on the temperature gauge. It will probably take a while to warm up- mine normally takes at least 15-20 minutes. Have the fan on and temperature set to max, but ensure the fan speed is set to its minimum value.

The thermostat should begin to open around the 82c mark (assuming stock thermostat, you should start to feel the bottom of the radiator and the lower hose get hot somewhere above 82c), and the coolant fans should come on at 95c. Wait until the fans come on and the temperature drops to their turn-off temp at 90c, and then you are done! Make sure you add a bit of extra coolant into the overflow bottle to make up for any tiny bubbles that may be still trapped- these will come out continually over possibly multiple days of driving :roll: .

Doing everything above should lead to a near-perfect bleed every time, but if you see your temperature gauge start to move (happens at 104c) turn off the engine straight away and let it cool down a bit. You probably have a bubble still trapped behind the thermostat. Letting everything sit for 10-15 minutes allows some of the heat to soak into the thermostat, opening it and freeing any trapped bubbles. After 15 minutes start the car again and make sure the fans come on and the lower hose gets hot. If the temperature gauge moves again, turn off and let sit for at least 30 minutes to cool down and allow heat to soak into the thermostat. Then you should be golden!

Finally, drain the funnel and put on the radiator cap- being careful with the coolant in the funnel as it will be very hot. I have done this method 4 times now, and each time it has lead to heat from the heater core and a hot lower hose first time, every time! It is time consuming and it does sound complicated, but these engines are very picky to your coolant bleeding method, and an incorrect bleed can lead to bubbles stopping coolant from flowing correctly through the whole loop! This is the quickest way to blow your HeAdGaSkEt :shock:

Sorry for the long post- but wanted to get this down in writing :lol: A picture of the radiator I am hoping to be actually enough for this car on track to hopefully make this block of text worth reading :lol: :lol:

Image
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Re: Considerations related to H6 head gaskets and cooling sy

Postby bigBADbenny » Wed Mar 10, 2021 7:56 pm

Love it! Comprehensive :good:
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Re: Considerations related to H6 head gaskets and cooling sy

Postby JezzaH6 » Wed Mar 10, 2021 8:59 pm

bigBADbenny wrote:Love it! Comprehensive :good:


That's the idea! Just wait for my DCCD writeup at the moment that's sitting at 3 pages :lol: :lol: :lol:

Trying to work out how to condense it without missing information.
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Re: Considerations related to H6 head gaskets and cooling sy

Postby bigBADbenny » Thu Mar 11, 2021 6:35 pm

Nah just do 3 posts :good:

Classic forum move is: reserved for updates :P

Hey you can kinda see why the oem rad is useful in some situations, there’s simply less of it, equals more airflow, or similar.
Iirc its related to heat soak, extreme ambient temperatures and possibly other heat exchangers in front.

Could ally end tanks be tigged to the stock core? Or just go aftermarket single row?
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Re: Considerations related to H6 head gaskets and cooling sy

Postby JezzaH6 » Mon Mar 22, 2021 9:16 am

It'll probably be more than that :roll:

I have noticed cooling performance is definitely not better in stop-start traffic (or low-speed driving in general)- I would attribute this to the thicker cores making a more-resistant flow path for cold air. Not like it overheats in traffic or anything like that but I have noticed it does seem to be hitting 95c and then turning the fans on more than it used to. As soon as the fans are on though the temperatures drop a lot faster than it used to, however.

IMHO I would guess that a double-core radiator in the 32-36mm core thickness would be a good compromise between day-to-day cooling performance and not having the car overheat. Even as it is with that thick boi I still needed to have the heater on, but with that on the temps were so much better that they were before! Will be very interested to see how it goes on track where the average speeds are higher than they should be through the hills!
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Re: Considerations related to H6 head gaskets and cooling sy

Postby nvmylh » Mon Mar 22, 2021 11:37 am

Hey Jezza I've noticed the same with my 25mm thick radiator. Sitting still will creep up in temps, as soon as the fans kick in OR I turn the AC on, they drop instantly.

Be interesting to see what temps your engine drops to when coasting. Mine will even go down to 79 on a long coast (say rolling off a freeway), on a reasonable 25+C day.

I'm going to look at getting the ecu to turn the fans on a little earlier.
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Re: Considerations related to H6 head gaskets and cooling sy

Postby JezzaH6 » Tue Apr 06, 2021 9:00 pm

Is that with the stock thermostat (starts to open at 82c) or the GT thermostat (opens at 78c)? I also played around with the thermostat in mine before getting the radiator made, but ultimately came to the conclusion that the stock thermostat isn't actually the cause of these cars getting really hot.

The fans are there for when the airflow isn’t adequate. The in-dash temperature gauge doesn't even move until the coolant hits 104c, so the fans keeping temps at or below 95 is the thermal design working exactly as its supposed to.

Having a cooler thermostat, or fans turning on at lower temperatures, doesn’t actually fix the problem. The issue is the stock radiators of these cars just don’t have enough surface area to support an engine of this size in Australia’s hotter conditions once you start to lean on it. IIRC the ecu turns the fans off anyway no matter the temp once you are going faster than 60 km/h, so on a mountain drive and especially on track, where I started to run into issues, changing the fan temps isn’t going to see a reduction in temps.
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Re: Considerations related to H6 head gaskets and cooling sy

Postby JezzaH6 » Tue Apr 06, 2021 9:50 pm

Are you running any oil temperature or pressure gauges? I was running into issues with the oil being too cold when I was running the GT thermostat- with the coolant around the 80c mark on the highway my oil temps struggled to get above 68c. This mean the pressure was over 100psi cruising at 100km/h. Pressures this high can cause damage and oil consumption.

After swapping back to the stock thermostat, with that big radiator and an air-oil cooler (also thermostatically controlled) I'm now seeing oil temps around 85-90c and pressures at 85psi cruising at 2700rpm. I've noticed less oil consumption after doing this, the engine revs a lot smoother and faster and the fuel economy is better not that the oil isn't so cold.
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Re: Considerations related to H6 head gaskets and cooling sy

Postby nvmylh » Wed Apr 07, 2021 9:18 am

I'm running the 21200AA072 thermostat, opens at 76-80C, full open at 91c. My oil temp will usually lag behind the water temp by 1 or 2degrees once warmed up and never stabilise at <70C. 68C when cruising at 100km is pretty cold!

I'm about to install a sandwich plate and oil pressure guage so will know more then. Hopefully my (hot) oil pressure isn't too high! I haven't noticed any oil consumption or excessive fuel usage (seem to average 11.2lt/100km around town), but I am cautious of winter, my engine might never get hot on my short drives to work (3km..)

What oil are you running? Pretty certain I put 10w40 semi-syn penrite in on my last oil change. I'll let you know what the oil pressures are like soon.
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Re: Considerations related to H6 head gaskets and cooling sy

Postby JezzaH6 » Wed Apr 07, 2021 10:39 am

That's very interesting. After reverting back to the stock thermostat I'm now seeing oil temps a few degrees above the coolant temps basically all the time. I wasn't happy with 68c on the highway not one bit!

Will be very interesting to see the results on that. Haven't really seen much actual data on this sort of thing posted by people so it would be good to see how my results compare!

Been running Motul Sport 5w40 basically from when I started looking into this data!
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Re: Considerations related to H6 head gaskets and cooling sy

Postby Yowie » Wed Apr 07, 2021 4:36 pm

Will be very interesting to see the results on that. Haven't really seen much actual data on this sort of thing posted by people so it would be good to see how my results compare!


Thanks for posting your observations Re oil temp, pressure, oil grade and then-current driving conditions.

I have a water & oil temp digital display and I ordered an oil pressure gauge on Monday night, so (once the later is installed) it will be interesting to see how my patterns compare to what you and others describe.
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Re: Considerations related to H6 head gaskets and cooling sy

Postby JezzaH6 » Wed Apr 07, 2021 8:53 pm

Not a problem. Always good to see if my results are at least somewhat close to what other people are seeing- especially as my engine has been DIY'ed by me myself and I (and a few mates lol). It seems the people who are really playing around with the H6 either have crazy money and don't really know what has actually been done to it, or just don't want to/aren't able to share much if any data. Doing my best to document all the DIY stuff I've been playing around with, even if my work and uni schedule makes it hard to actually write anything up in any sort of useful timeframe. Maybe that's a third reason re above :lol:

Would be very very interested to hear what your experiences are!
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