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PostPosted: Tue Oct 09, 2012 8:40 am 
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Been losing coolant (water + water wetter) for some race meetings now. Varying quantities. Have switched from standard header tank to a high mounted one ex Alfa 33 and modified the system with the return in the lower radiator hose per other recent threads (I also run a Porsche 944 alloy radiator). Still unable to locate the source of the leak as under bonnet race temperature simply evapourate everything. So, put a blue dye in and then went racing last Saturday. Water and oil temps both no higher than 85-90C all day as weather cold and windy. It came as a surprise that the system was under quite some considerable pressure (hoses very hard) given the low temperatures. Previously on hot days with higher temperatures I hadn't been concerned by this. Initially I noticed dye all round the header tank cap but strangely when got home found small traces just about everywhere that water could escape. The further back the bluer everything got - bell housing and gearbox were the worst

I'm now left wondering if the water leak is the result of the systen getting pressurised rather than the problem itself. I thought a leaking head gasket so I borrowed a cylinder leakage plews tool - all cylinders gave the same result under pressure - no bubbles in the water and the only apparent 'leak' on each was past the rings into the crankcase.

Engine spends most of its life between 5500-7000rpm so I wondered about pump cavitation, but could this pull in air and pressurise the system to the extent it blows past a 15psi cap?

I'm stuck now so would appreciate thoughts and ideas. Next meeting is at Manfeild, a 5-6 hour drive away so I want to get this sorted before going all that way!

Geoff


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 Post subject: Geoff.....
PostPosted: Tue Oct 09, 2012 9:09 am 
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If it was me the first thing I'd try is a new expansion tank cap.

The standard system adapted to include an improved expansion tank does generate quite a bit of pressure.
When the coolant has cooled (overnight) the level appears below to have dropped but on releasing the cap it rises back up.

In theory you shouldn't suffer pump cavitation because you have the expansion tank plumbed into the bottom hose.
However I note that Saab attempted to cure cavitation with a redesigned impellor.
(I have one of the six vane Saab pumps on my 1850, it fits under a later Sprint/1850 12 vane pump cover.)

Another suggestion I have is to use upgraded hose clips.

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PostPosted: Wed Oct 10, 2012 12:37 am 
Hi Geoff,

It sounds like the cooling system could be building up excessive pressure maybe from a head gasket leaking when the motor is hot. I would suggest fitting a pressure gauge to the cooling system. We have always run our race cars with a pressure gauge (0-20/30psi) fitted to the thermostat housing. It seems to give us more information than the temp gauge.

1. If everything is normal water pressure seems to run around 5-10 psi.
2. If the pressure never rises there is a continaul leak in the system.
3. The system should hold pressure after shut down (30 minutes).
4. As motor revs water pressure will rise slightly but blown head gasket will show under load with excessive pressure.
5. During racing you can watch the pressure. Even if the motor is hot providing the pressure is stable and under the cap pressure the cooling system is still intact.
6. If the pressure rises to cap pressure and than falls it shows that the cap has lifted and you are loosing coolant.

it is a worth while instrument (tool) and certainly helps to diagnose cooling system issues.

Good luck

Mark


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PostPosted: Thu Oct 11, 2012 10:50 am 
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Thanks Mark, I've looked unsuccessfully in the past for special gauge with a low pressure range like you describe. Did you have to put one together or is there one on the market? I'm assuming it is mounted so it can be read inside the car?
Geoff


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 Post subject: How about.....
PostPosted: Thu Oct 11, 2012 7:25 pm 
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A trip to a plumbing supplier...?

http://www.ebay.co.uk/itm/Low-Pressure- ... 649wt_1173

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PostPosted: Fri Oct 12, 2012 8:15 am 
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Thanks everyone. Found a gauge, fitted but will obviously now have to wait until back on the track as all I could get it up to was around 8psi and 85C. No leaks of course.

Been out on the road since and even a 4km hill at 5000rpm in third only pushed it to 10psi. Then sitting on the drive at 4-5000 rpm pushed it up to 13 but no more. I then let it settle back to 8psi and switched off. Still retaining 4psi pressure some 30 minutes later. Looks all good, but no sign of why it lost water previously.

Geoff


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PostPosted: Mon Oct 15, 2012 10:56 pm 
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My guess for what it might be worth is a slight HG leak of combustion causing small amounts of coolant to be expelled at any weak point.
A modern expansion tank that returns coolant into bottom hose helps slightly.

Good luck.

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PostPosted: Mon Nov 12, 2012 7:06 am 
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.. and the answer is a slight leak on both Nos 1 and 2 cylinders into the water jacket. It was getting worse as the race meeting Sunday before last proved. So much so that water was getting back into the cyl and in the last couple of races in the final laps caused a misfire at high revs starting as I changed from 3rd to 4th.

Took the head off yesterday and the evidence was compelling - also appears that water was gettingpast the gasket to the outside - still some blue dye left that showed up well.
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Some work to do now. I'll also rebuld the water pump to 6 vanes - some more issues here but I'll post those on the general forum.

Thanks everyone.
Geoff


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