jwyatt8171

Hey guys,
I was driving today, and noticed my temp was @170f a bit low, as it usually runs 190ish, the last mark before orange on the s4 gauge. Watching it it shot up to 180 rather quick, less than a second. Then I noticed it move a few times alot faster than it should, but staying between 170 and 190.
I have hadn't boil over three times in the past year, but the gauge never shows it's hot.
What's the best method to verify all air is out of my cooling system? Anything else I should consider as well?

Thanks for the great help and guidance on this board. I is valuable and appreciated!

GregBBRD

Self bleeding system. As long as the reservior stays full, there will be no air in the system.

An S4 shold never boil.over. Never.

If it does, there is something very wrong.

Snark Shark

Does your reservoir ever overflow and need to be topped off? That's how you know there's air in there. The air bubble expands way more than the coolant as it heats up.

jwyatt8171

Thanks for the input Greg. I hold your opinion in high regard.
I do not drive the car much. I avoid it when the temperature is over 88 or so. The few times I have driven in hotter days the temp seems to run a little over the 190 mark, and at times seems to approach the orange mark. When I stop the car i hear it boiling. I loose some coolant through he overflow tank at this time.

I do think the overflow tank is low right now, and may be contributing to the temp gauge bouncing some.


I am using the 928motorsport alum overflow tank. I'm not sure where the top level is, so i fill it up. That may be a problem...Hell i don't know.

I definitely don't want to cause any issues.

Snark Shark

I think you should try a new reservoir cap or get a pressure tester to make sure it's holding pressure (however much the cap is rated for). If the system doesn't hold pressure that could cause local boiling. I wouldn't drive it until you do that, since it could cause warped heads or a blown head gasket. It's also possible you already have a blown head gasket, and exhaust gasses are creating a bubble.

GregBBRD

The idea of an overflow tank one can't see through baffles me....impossible to monitor the internal level, which is of utmost importance. If I was you, I'd order and install the correct overflow tank, so I could tell what was happening.

On an S4 both cooling fans should run st low speed until the engine gets near the orange zone. Once near the orange zone, both fans should switch to high speed (which is very loud.) The temperature should drop very quickly, once the fans switch to high speed.

If you temperature gauge is anywhere near correct, you should not hear boiling noises until it is deep into the orange zone.

Are you running coolant in the system to raise the water boiling point? A minimum of 40% coolant to water is needed.

Does your radiator cap on the reservior hold oressure (coolant boils at a much lower temperature without pressure).

If in doubt, order a new Behr cap with a new overflow tank.

FredR

The purpose of the tank is to allow the coolant to expand thus if it is full it cannot do this without puking out of the cap that is designed to release excessive pressure [i.e. anything over 15 psig]. Liquid coolant is non compressible so if the tank is full for sure some coolant will be lost. When it cools and contracts the cap is designed to allow air into the system to prevent a vacuum forming.

Thus as the motor heats up the air space in the tank compresses and pressure builds up. The pressure allows the coolant to operate at a higher temperature before it will boil. All being well the coolant should not reach its boiling point. Thus why the level in the tank is critical to successful operation of the system.

If your coolant is boiling then something is very wrong. The stock 50% coolant at atmospheric pressure will boil at about 108 degrees C and at 15 psig will boil at 129 degrees C.

The stock cooling system holds about 45 litres [that is 12 US gallons, 48 US quarts or 0.12 bathtubs full] and if the temperature rises from 20C to 90C, the volume increase will be approximately 1 litre assuming an average CTE [coefficient of thermal expansion] of 0.0004 /deg C. Thus the tank has to have an expansion volume greater than this amount above the level when the coolant is in the cold condition. Note: this number is indicative as I do not have accurate data for the CTE but I would expect it to be accurate to within about +/- 25%.

For your system to work correctly and efficiently, the first thing to look for is the thermostat and the integrity of the rear seal. If this seal fails some of the coolant will circulate around the water jacket as opposed to passing through the radiator.

As I can tell the 928 cooling system does not reach a point where the coolant can boil such is the efficiency of the system and if it does, this may be an indicator that something is not working correctly. Using a leaner mix in the coolant improves the ability of the coolant to pick up heat and reject it. I typically run a 33% mix as I do not need to worry about freezing. Indeed this is why many racing engines run 100% water for coolant with corrosion inhibitors and then drain them after the event is over. No problem as long as the coolant temperature does not reach boiling point. Similarly throwing in some water wetter also helps heat pick up and rejection. Beyond that heat rejection can be improved by fitting a bigger radiator and [to some small extent] more powerful fans.

Thus if you suspect your coolant is boiling up the first thing to check would be the thermostat and its rear seal. I have had my system not holding pressure and yet still ran with no issues because the coolant was not boiling up.

When the system is holding pressure, if the cap is released it will hiss as the pressure is released but as yet I have never seen it boil up. If this condition does happen it will spit coolant out all over the place- potentially very dangerous especially if you do not cover the tank with a cloth to catch it. Other cars I have owned will do this but not the 928 when all is working correctly or so my experience suggests.

SeanR

Are you running the fan set up of Carl's that has two tiny fans on the drivers side only?

jwyatt8171

Yes, I am running the 2 small fans on the back side of the radiator, but I also have a large pusher on the front side as well.

The PO had the SC installed, 928MS radiator, aux cooling fan, and expansion tank.

Carl Fausett

Oh boy... here we go.

NO, he has three fans running, two 8" fans on the inlet side of the radiator where they can do the most good, and a large pusher fan in the front that you can see in the picture.

I do not recommend running 4 small puller fans on the back of the radiator as it is not needed with our kit. We do not block off air flow through the radiator like other kits do, and because of this the entire radiator is still available for cooling.

Those that have installed 4 small fans in the back, plus a pusher, and perhaps even a 6th fan on the heat exchanger in the fender well (Stage II, intercooled) have fried their alternators trying to keep up with the 120 AMP draw (6 fans at 20 amps each) all these fans cause. Just repaired an engine wiring harness from one of these cars recently and the insulation on the wiring to the positive post was melted off!

So we designed our kit not to need so many fans to maintain the proper air temp.

Carl Fausett

I agree with Greg - the system is self-burping. There should be no air in the system if all is well.

I disagree with Greg - regards the opacity of the coolant reservoir. After a few years, the plastic is so yellow its opaque anyway. Plus it cracks. You cant see though an old plastic reservoir either. Do what we all do on all our other cars - remove the radiator cap and LOOK.

Lets please start at the basics rather than shouting out wild ideas about numbers of fans and opaque coolant reservoirs.
Don't guess - TEST.

DO have a mechanic place a STANT pressure tester on the coolant system and verify the system is not losing pressure nor fluid.

I agree with Greg that an S4 sould not overheat. If it does there is something wrong.

It could be you are losing fluid down to a level where you over-heat, then you top it off and the problem goes away again until it looses fluid to that low level that it overheats again.

It could be head gaskets.

It could be a bad thermostat.

It could be your radiator cap is no longer maintaining pressure to prevent the coolant from boiling.

There are others. But lets start with simple diagnostics and see if everything is healthy.

BTW: damn nice looking install! Do not hesitate to contact us for tech support on your supercharger kit.

dr bob

Sometimes we overlook stupid-simple stuff in our quest to be the one to come up with the most complex diagnosis. Carl's suggestion reminded my that one of the main places for air to be drawn into the cooling system is at a failing reservoir cap. Coolant expands as it gets warmer, and if the cap isn't holding it will push some out of the little reservoir vent tube well short of overheat temps. When the engine is allowed to cool, the little flappy check-valve in the cap allows air back into the space where the coolant was. Caps are cheap. Get a genuine Behr 1-bar (~14 PSI) cap if you can. Our regular vendors have them.

If you have the original reservoir still in there, most are getting to the point where there's a risk of a crack in the tired plastic.

FredR

When I read the initial post and the first few responses I tried to stimulate some discussion to see if others might agree with a couple of points I noticed [post 7] but to date that has not happened.

The bit about the expansion tank cap working correctly is perfectly appropriate and has been mentioned several times but the OP has not responded to that so presumably he does not know whether it is holding pressure or not. I suspect that given the excellent condition of everything whoever installed this kit would have fitted a new cap and not too long ago but of course that could fail as could a number of items. I also note that the cap fitted is one of Carl's specials but I have no idea whether it is the 7 psig "low pressure" model or the 20 psig "high pressure" model. That Carl perceives a need for both these options is interesting in its own right.

What struck me initially was that on his own admission, the OP did not know what level to fill the expansion tank to so he filled it right up [or so I understand]. Whereas this is not a good thing, the system [if working correctly] should correct itself by blowing off the excess coolant and then pulling in some air when it cools. Perhaps the OP can clarify whether he checked the level and then when it had dropped, whether he put some more coolant in to "top it off". If he did this that would confirm the cap was holding pressure- that or there is a leak somewhere else in the system. Either way the OP needs to ensure that the system holds pressure and that the cap is holding.

Regarding the use of Carl's expansion tank, the only thing I would add is that as I alluded to earlier, level in the expansion tank is critical to system performance. If the level is too low the system will not build pressure as it should, if it is too high it will likely puke coolant out [or blow something if the cap does not lift]. The stock tank has high and low level lines so the user can gauge where the level should be and that is quite a narrow band. If it does not have such info supplied, perhaps Carl might consider specifying what depth to set the level at - probably somewhere around the half full point? That or fill the tank and then remove a proscribed amount [1 litre?].


The other interesting bit of info was how the OP perceives the system cannot cope to his comfort on what he perceives to be "hot days". 88F corresponds to 31C- what I would call "a nice day". My system can cope with 44C "hot days" but then it is optimised as I alluded to earlier. A stock 928 should have no problem whatsoever at such temperatures but then this is not a stock 928, rather it is supercharged with Carl's Stage 1 kit that adds about 30% [?] extra power and proportionate additional heat to get rid of. For street use with the occasional cavalry charge I would expect this to show an increase in temperature but nothing too dramatic. So the question here is whether the reported symptoms are excessive or "to be expected"? In my opinion a lot of folks get over excited when they see the temperature go up a bit on the dash indicator. However there is a reason why the dash panel indicator shows a red section and also has an alarm in the separate annunciator panel. If that alarm goes off take serious note and shut down the motor quickly until you fathom out what is wrong!

Even on my stock motor with modified cooling system I have seen the indicated temperature go up when working the motor on "hot days"- i have seen it north of the last white line and it never bothered me because the system was "under control" but operating at a slightly higher temperature. I have also seen [twice] what happens when the water pump impeller falls off- no mistaking that one!

Greg also mentioned that to maximise the boiling point the coolant mix has to be maintained- this is correct and max boiling temperature occurs with something like 60% glycol. However this has to be conditioned by the fact that glycol reduces the ability of the coolant to transfer heat. The system can get rid of more heat at hotter temperatures [more driving force] but if it picks up less heat that benefit can be lost compared to the heat flux carried in a leaner coolant mix. The other option is to add water wetter- this also improves heat pick up and rejection rates- in my case I found that 33% mix with water wetter seems to work well supported by a better radiator [the OP has Carl's radiator- good].

So, assuming the OP can get the right level in the expansion tank- is his system problemmatic or is it working as intended? Having air in the system is no problem as long as it is where it should be- in the expansion tank. If the coolant is boiling up that is not air it is steam [very bad]. If the temperature indicator is around the 190F [88C] mark how can the coolant be boiling?

Snark Shark

Maybe it's not boiling. Maybe he's hearing air being sucked in through a leak.

That's what my car was doing until I replaced the cap and fixed a leak. Shut off the engine, the water cools and contracts and air gets sucked in through the leak. I couldn't hear any sort of boiling noise, but it was a tiny leak.

928NOOBIE

Sounds like you have a pressure issue. I'd start with a brand new radiator cap. I was having rapid temp swings on my needle as you describe. The new cap eliminated that. My cap looked fine...so yours may too..as a previous poster indicated...it's the ability of the spring to withstand the pressure...and that's a punishing environment...I learned my lesson and my car is getting a cap every 4 - 5 years ...they're $15 bucks for the correct Behr cap...get the correct one, as Greg indicates.