mark kibort

Just a data point... i went out last night to do some testing and came back and measured the time it took for the hoses to loose their high pressure. it took 15 mins before they were a little softer, but not ready for cap removal. (still pressurized). 30min and it seemed like i might have been able to remove the cap..........but ive done that beforre and have it bubble up and raise water level... which means voids are created in the lines. Just wanted to make absolutely clear that the cap works fine.

Mrmerlin

best way to check the cap is put on a new one.

Its also possible the head gaskets may need to be replaced,
as the flow holes could be damaged.

These holes go from small to bigger as they go from front to back on HG.
Thus they may not be holding the coolant like fresh gaskets do.

mark kibort

Stan, again, why do you think there is a problem as the system hold fluid well. cap tests out obviously well. (i checked it with a pressure tester) .... i did another test. came back from some 60-100 runs and came in. fans were on.... (so it was warm) temp in the middle...... very high pressure in the lines. they stay high for some time.... during the cooling process, when they are still under pressure, if you loosen the cap , you get some boiling too, as you would expect..

why do you think the head gaskets need to be replaced. not losing water...... compression is perfect all cylinders,

you dont seem to understand, you can get any 928 to overheat at any time. and when it does , the fluid boils, fluid level rises, and will push out the over flow as it is designed to do....... cool it down by driving or fans and there will be no pressure in the system as soon as it gets to normal operating temp. this is pretty simple stuff.

if you disagree, tell me test that will show you that the system is failing in ANY way. also tell me how it would be possible for a system to boil, push fluid out and then cool and still be under pressure with the fact that the contracting amount volume would allow air to enter the cap and the system as it is designed to do...... Jim C was telling of a problem where his cap didnt work and ended up with collapsed holes (under vacuum). the other failure that can happen and you are eluding to, is a bad cap, but then that would mean its releaving pressure before it gets to the upper white line, and warning light, which it doesnt. again, there is NEVER a loss of water, unless the engine overheats. this has happens at T-hill with a 100 degree day and air in the line to start..........(where this topic started), then i had a 115degree race, and it overheated there with temps never seen before at laguna for 20 years.. and then i overheated in my "Garage Dyno" tests with one fan not working and ton many successive runs.. Ive had some hot days racing in the last 4 races, and the car runs cool as it always have, making sure the engine has no air in the system before start up is key. Ive also cut out more cooling inlets so that there is even better air flow this season.

as a side not, i was chasing an over heat about 15 years ago, and i ended up having a cracked overflow bottle..........replaced that , and the problem went away.. Ive had intermittent working water pumps (slipping impellers) , ive chased down proof of that by hijacking the thermostat (pinning it open) and running water from a hose into the engine and out of the engine (like an engine flush). proving pump was working or to prove the radiator was not clogged. Also, i have had sticking Tstats and laking T-stat seals.. So, in other words, i have quite a bit of cooling system testing, evaluation and assessment experience.

Mrmerlin

So, in other words, i have quite a bit of cooling system testing, evaluation and assessment experience.
__________________
Mark Kibort
1987 928S4 - SCCA Sears Point Race 2013







well I guess you dont need my assistance

mark kibort

I love the discussion and always welcome constructive criticism....... The original post was to help anyone that was going to not completely remove air after a recent water fill, or a recent boil over , in that it can compromise the system and ruin a track day or cause an overheat under high performance activity. it was also to show that i was able to replicate many others thought was an indication of a problem... I dont see a problem in what i have shown. If there is something I've missed or mis-assessed even though i do have many hears of "experience" working with cooling systems, i would certainly want to hear about it.

what part of the description of the observation to you find to indicate that there could probably be a problem?

Mrmerlin

Maybe if I am in CA,
I will come watch you race .
Keep em flying,
good luck on your racing season

vze2jshn

Porsche engineer at a Porsche Parade years ago: "The 928 engine is not a racing motor".

mark kibort

200 races...... 100s of racing hours.....7 pro races. 100,000s of miles of street driving. seems that the porsche engineer made a little underestimation. i guess its how you define "race engine"

Here is the stock 928 engine before mods--------

Listen to this: