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Discussion Starter #1
Evening all,

Keep having a problem with my cooling system when i go on track days. On the road the cooling system acts and performs 100% as it should, thermostat opens, fan kicks in etc.

Now every time i go on track it fills the expansion tank up, sometimes so much so it leaks from the top and i find alot of air in the system. I have an aftermarket water temp gauge so i can keep a good eye on temps. I general pull into the paddock if the temps get between 95-100 degrees celcius (203-212F) due to this problem, that should be a fair bit below boiling point.

I'm running a skunk2 Half rad but this used to happen on the stock full length rad also. The thermostat has been replaced with a brand new honda item with 2x4mm holes drilled in it to aid bleeding the system and the rad cap is a brand new 1.3 bar item. The coolant is Motul inugel optimal premixed stuff, of which i have bled as best i can. I have also performed a sniffer test on the coolant to see if it was a HG problem of which tested out okay.

Does anyone have any ideas on what may be causing this? When on track i drive it quite hard as its relatively low powered so i can get on throttle alot, however i'm only ever out for 15-20 mins at a time, mainly due to this problem.

Any ideas/experiences would be great,

Thanks Lee
 

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Brokedick Millionaire
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I had a cracked cylinder head around #3 spark plug. I could daily drive all winter without issues. But once in summer and stop and go traffic, it would push the coolant out when water temp got above 175 ish.
 

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Discussion Starter #3 (Edited)
My next step was to pull the head incase of as you say a hair line crack or the HG passing at higher temps, but wanted to check there was nothing im overlooking before hand.

One thing i will mention though is it will regularly reach 212F on the road as that is when the fan switches on and it acts absolutely normal.
 

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is it bubbling up in the coolant reservoir ? if it is its either a cracked head, or a bad head gasket, most likely a bad head gasket.

gl.

stratton.
 

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Brokedick Millionaire
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My next step was to pull the head incase of as you say a hair line crack or the HG passing at higher temps, but wanted to check there was nothing im overlooking before hand.

One thing i will mention though is it will regularly reach 212F on the road as that is when the fan switches on and it acts absolutely normal.
Fan should be coming on before 212, 200-205 on, 195-200 off....depending on gauge accuracy. One thing I do like about OBD-2 :)
 

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Discussion Starter #9
Evening all,

To report back on this, i pulled the head and sent it off for machining and had .060" off the deck face for compression, bolted it back up with ARPs and a genuine honda z6 gasket. I couldn't see any cracks in the combustion chambers and unsure if the machine shop checked for cracks, but they're very reputable so i assume they would have noticed something if there was something to notice.

Now i went to brands hatch yesterday and the car was holding good temps all day varying between 82-95 degrees (180-203), it only got into the 90s when i was really pushing the car. However on my last session which also happened to be were i pushed the hardest, when i pulled into the paddock the expansion tank had filled to about 3/4 full. Is this normal? As on hotter days i can see temps being higher and subsequently system pressure being higher aswell. I've come home and checked the expansion tank today and its sucked some off the coolant back in as expected but not all of it(i kept it filled to the min level and after sucking it back into the rad its halfway between min and max in the expansion tank). However i poured what was left in the expansion tank back into the radiator and it did not fill it to the top albeit not far off, so it seems ive lost/boiled some off. I am almost 100% i have no leaks so im a little baffled.

I've just added an Mfactory LSD so when i wasn't on the brakes i was pretty much on the throttle, im wondering maybe the water pump is cavitating with all the sudden changes in speed or potential hot spots in the engine causing steam and excessive pressure.

Can anyone add anything or have any ideas? As i've changed everything now yet i'm still getting the problem, im starting to wonder if i should add a swirl pot to the system of maybe even an electric water pump to keep the coolant flowing faster and keep any potential cavitation at bay. I'm a bit dubious about both ideas however as i thought it would be a more common problem.

Any advice/ideas would be great, all i want is a reliable cooling system so i can take the car out and beat on it time and time again.

Thanks Lee
 

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Discussion Starter #10
Just to add the motor revs to 8000rpm and has a 4.4final drive installed, so it's almost always in the later half of the rev range 5-8k.
 

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So the head wasn't pressure tested during this latest visit to the shop? Was the block decked during the initial build? How many times have you re-torqued those ARPs?
 

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Classic Man
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A very small leak in your cooling system will cause what you talk about to happen. Also a bad radiator cap.

If the system doesnt seal 100%, when it cools down it will suck in air from your leak, instead of sucking the coolant back in from the overflow.
 

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Discussion Starter #17
So the head wasn't pressure tested during this latest visit to the shop? Was the block decked during the initial build? How many times have you re-torqued those ARPs?
regrettably no, never again! i only re-torqued them once after a few heat cycles and about 50 road miles. None of them needed it, all clicked instantly.

Did you re-tune the engine after milling the head 1.5mm?
If you didn't - you are are getting det 100% and that's causing the blown hg. http://www.d-series.org/forums/diy-forum/104254-diy-stethoscope-det-can.html
Also - is the block decked?
Block wasn't decked as i only pulled the head, runs a mechanical dizzy so un-tuneable essentially. Again regrettably i should have checked it for straightness. I checked the AFRs which were all good(its a carbd motor), i also run premium fuel 99ron i think its equivalent to 93 in the US.

Skunk 2 makes a 1.3 bar cap. Others have had issues with weak caps but usually it isn't the problem.
A very small leak in your cooling system will cause what you talk about to happen. Also a bad radiator cap.

If the system doesnt seal 100%, when it cools down it will suck in air from your leak, instead of sucking the coolant back in from the overflow.
Already has a 1.3bar rad cap, and almost sure it has no leaks. Never seen any residual coolant and i'm forever under the bonnet.

I'm starting to point my finger at the head gasket again, will do a sniffer test and coolant system pressure test later in the week. However i couldn't see any noticeable head gasket failure on the last gasket.

However i am 100% going to add a swirl pot to the system to aid future bleeding and preventing gas introduction to the coolant system.
 

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Are you running allot of timing up in the high rpm??' 8000 rpm with more timing will cause cylinder pressure high enough on a d series to overheat and blow the hg.... Cause the waterpump is geared differently from the b series also it can act weird if the tune is too aggressive.... Take out the thermostat and connect the fan directly and then do a lap... See if anything changes... It can help you determine where to look... Most likely a hg
 

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Discussion Starter #20
Are you running allot of timing up in the high rpm??' 8000 rpm with more timing will cause cylinder pressure high enough on a d series to overheat and blow the hg.... Cause the waterpump is geared differently from the b series also it can act weird if the tune is too aggressive.... Take out the thermostat and connect the fan directly and then do a lap... See if anything changes... It can help you determine where to look... Most likely a hg
I have an aftermarket temp gauge in the car, its not a heat issue as such.

The block had a 2 thou dip in between the cylinders in the end, i put a spare stock motor in it and had the same problem. Will have it machined flat and go again im confident that's whats caused it though.
 
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