There's a big difference between having the needle at the third white line and having a boil-over.

If my feeble estimation is correct, the line on my S4 gauge between the 170 line and the 210 line is about 190. The target operating temp for the car is between 185 and 190. A little lower or a little higher is no reason to panic, so long as it's steady there. The thermostat and the fan-n-flaps controller work together to keep the temp at about 190. We might look at the gauge and think it should run a lot lower. It shouldn't. We put lower-temp thermostats in thinking it will cause the car to run cooler. It doesn't, at least not on its own.

Does your car boil over? Find out why. One of several possible causes is the thermostat, but it's a really rare cause. More likely is a partially-plugged radiator. Poor coolant quality and/or a poor history of coolant quality. Fans that are tired or not working correctly. Poor airflow due to debris buildup. A poorly-sealing or tired coolant bottle cap. The car can boil over at an indicated 210 degrees or less if circulation is poor. You can boil coolant in the block while the sensor and thermostat in the bridge see cooler temps. All it takes is poor flow in the block, or an air bubble in the bridge.

 

Radiator cap? Old/bad ones will not hold pressure. Cheap insurance.

 

The engine trays significantly improve airflow and engine temps are measurably cooler according to Landsharks.

 

I've tried every thing mentioned here, and potential bad parts have been replaced with brand new (radiator, all sensors, thermostadt, coolant, cap, system clean throughout, and so on). It does run cooler but not cool enough to keep from boiling at heavy load in hot weather. I sense that if the AC cooler weren't there or the thermostadt would let just a bit more H2O through, that would be enough to make the difference. The AC unit fins are straight and clear and the Thermostadt is opening and sealing like it should. I know it must be something pretty simple but just haven't stumbled across it yet.

When it gets to speed it does cool down a bit but not nearly as much as I thinki it should, which would seem to point to air flow..hence my initial inquiry. It does have a replacement AC radiator unit. Perhaps it's the wrong one and is too restrictive? But it would seem to let ample air through.

Thanks,

H2

 

Colin will you share where this info comes from?

 

Harvey:
Replace your radiator temp sensor and your thermostat with 72 degree units and you will be happier.

 

I had a old Corvette years ago that ran warm all the time. I drilled 2 holes in the thermostat to allow SOME water flow at all times...It helped. ???

 

that would cause hotter temps in a 928 because it would cause some water always to bypass the radiator.

 

It depends on where you drill I guess. If you drill the rear disk, the one that pushes against the suspect rear seal, then you increase recirc and bypass the radiator. Holes in the front main disk will allow (but not 'cause') coolant flow through the radiator prior to normal thermostat opening. That would slow the warmup some but will not cause the car to run cooler.

DIY'ers need to be aware that the thermostat provides a planned restriction in the coolant flow when the engine is at temp. Absent that restriction, low pressure in the block may allow localized boiling where there are hot spots. Those hot spots grow due to lack of coolant contact, until the engine is overheated. Not good! American-car hot-rodders will tell you about the dangers of running without a thermostat, but they will try to tell you (incorrectly) that the heating is because the coolant circulates too fast in the system. Anyway, don't spend time dinking with drilling holes. It causes slower warm-up, but meanwhile the thermostat compensates for any lower temps it might see at load by bypassing more coolant around the radiator.

 

Did I miss, in your list, that you have checked your flaps in the front bumper cover to ensure that they are open fully? Closed flaps will cause a 928 to get way to hot at speed.

You have no MY in your signature, but IIRC you have a <'91 and therefore have (or had) flaps.

 

Here it is:
Stock flap delete? As in from the factory? What MY?

 

I know this might sound silly, but how's your timing? A few degrees off can cause the motor to run a bit hot.
Please ignore this comment. I forgot you have an s4 now. Doh!

Good Luck.

 

Hello,

below is an excerpt from my FAQ page that I wrote for Jaguar v12 engines which have cooling problems , the same info can be applied to any engine:

The v12 Analogy
Think of a v12 engine as you would think of a freight train. If you were driving a Freight Train you wouldn't put the brakes on when you get to the station, you would put the brakes on a long way before you get to the station.

This concept applies to the v12 engine. You wouldn't start your cooling fans when you reach operating temperature, you would start your cooling fans before you reach operating temperature. There's a lot of metal and a lot of fluids that need to be cooled and it can't happen instantly.

Fan 101 Guide by v12s
or
Truth vs Marketing
Some fan sellers appear to defy Ohm's Law when describing their fans, apparently they haven't heard of Ohm's Law.

As an example, a 14 inch fan with a 90 watt motor draws approximately 7.5 amps, not 10.2 amps, at 12 volts DC. The same 14 inch fan with 90 watt motor draws approximately 6.7 amps, not 10.2 amps, at 13.5 volts DC. Check out Ohm's Law to determine if the fan seller's claim's match the fan being sold.

Some fan sellers promote CFM as being the only important consideration, but it's not.

As an example, a 16 inch fan with a 250 watt motor (apparently only 10 amps at 13 volts?) - is claimed to generate over 3600 CFM at zero static air pressure- that's 3,600 Cubic Feet of Air Per Minute, or presented another way - enough power to move all the air out of a room that measures more than 22 feet by 20 feet with an 8 foot ceiling in just 1 minute - what load of bull!

Here's another good joke - a 13 inch fan with an 8 amp fan motor (about 100 watt motor) claimed to pull 2900 CFM, more bull, divide the CFM by 2.

I would welcome fan manufacturers enlightening me with their scientific proof but they ignore requests for independent lab data showing their CFM figures, in fact one fan manufacturer specifically told his sales rep not to talk to me - they can't handle having their claims challenged. I plan to do my own tests in the near future and display the data here for the 'popular' fans currently available.

A word about quality: there's plenty of cheap $5 fans available that look the part but are nothing more than mere inferior copies of brand name fans. The quality is like those 1-time-use kids toys that they dump on us here in the USA. Did you know that the plastics used in cheaper fans are inferior polyproylene mixes? This makes these inferior fans less impact resistant and less capable of coping with high temperatures - ie. brittle. Quality cooling fans are made with plastic composed of glass-filled nylon. You get what you pay for, right? Some people don't care about what they sell to you, we do, we give a lifetime warranty, every fan supplier should give a lifetime warranty - don't buy a fan without a lifetime warranty.

I've built over 1,000 electric cooling fan assemblies for v12-engined cars and others, so I have some experience in choosing the right electric fan and weeding out the fact from fiction. My fans are 70% more powerful than the common fans available elsewhere. So, here's what I look for when choosing fans.

Firstly, some things to think about before buying an electric cooling fan:
- does your car have a/c condensor mounted in front of the radiator?
- does your car have a seperate oil cooler mounted in front of your radiator and/or a/c condensor?

A 10 inch fan with an 80 watt is fine for most applications where only a 10 inch fan could fit - this excludes all V8, V10, V12 and bigger engines.

A 14 inch fan with a 90 watt motor (most 14 inch fans on ebay) that spins very fast may be OK if you have a thin radiator and no A/C condensor or other coolers in front of it - it's not OK for a V12.

If you have A/C then I would choose a fan that has a 120 - 160 watt fan motor.

If you have an A/C condensor and another oil cooler in front it then you would want to use a fan that has a 160 - 225 watt fan motor.

When you bought a 'shop vac' what did you buy? The weakest or the most powerful?

Of course current draw is important, but that doesn't mean sacrificing engine cooling. If your classic doesn't have enough amps to get the job done properly then buy a more powerful alternator and battery. Destroyed engines due to a lack of cooling, especially in classic cars, are an expensive and foolish error.

And what about curved blade fans versus straight blade fans? The patent for curved blade fans only claims that they are quieter than straight blade fans, there are no claims of more airflow (all things being equal).

In conclusion, this Fan 101 isn't meant to cover everything but it is meant to highlight some fact from fiction.

Q. Which type of fan system is best?

A. We only build fan systems that draw air through the radiator, sometimes referred to as 'puller fan systems'. This is most efficient.

Systems that try to push air through a radiator face two problems: 1. they're only about 80% efficient because the radiator deflects at least 20% of the air, and 2. the fans themselves actually block the airflow to the radiator, whether the fans are running or not. Our fan systems work better.

Q. What are examples of 'Normal' temperatures on a V12 XJS?

A. These temperatures recorded after a normal drive - summer, 88F.

Top radiator hoses - around 192F
Oil filter 210F
Exhaust manifolds 325-350F
Catalytic converters 358-393F
Exhaust tips 148-155F
Inlet manifolds 146-154F
Coolant overflow tank 195F
Valve covers 226-228F
Brake discs 206-211F

Use an infrared thermometer (minitemp NAPA) and compare your temperatures.

Q. What's the airflow difference between flat and curved blade fans?

A. How long is a piece of string...? - there are too many variables to give a definative answer to this question.

The patent for curved blade fans (S-Blade) only claims that the fans are quieter than flat blade fans; but the number of blades, the pitch, the strength of the motor and other features could make a curved blade fan output more airflow or less airflow.

We quote the standard manufacturer's fan motor wattage figures.

Q. Do I need a fan shroud?

A. Our electric fan systems are complete with a handcrafted shroud. A fan shroud will allow your electric fans to draw air across the whole surface area of your radiator. If you simply attach one or a couple of electric fans to your radiator core without a shroud then you will reduce your ability to cool your engine by at least 30% - 40% or more.

It's a big mistake to simply insert an electric fan in an old mechanical fan shroud and attach it to your radiator as the shroud is now ineffective.

Q. What's the difference between a 'Dual' and 'Twin' Fan System?

A. A twin fan system has two fans that are identical in size and performance, a dual fan system has two different size and performance fans.

Q. Should I use a thermostatic switch with a relay?

A. Yes. Our optional Thermostatic Relay Systems include thermostatic switches. A thermostatic switch to control your fan relay(s) will: 1) allow faster engine warm-up, 2) prevent battery drain by cycling the fans on and off, only as needed, and 3) extend the life of your electric fans.

Q. Will my engine run cooler if I remove the rubber shroud flaps?

A. No. It'll actually get hotter because the fans will draw air from these 'open' flaps instead of drawing air through the radiator core.

Q. Should I use colder thermostats?

A. No and don't remove your thermostats either! Your engine was designed to run at a specific temperature for emissions, performance and fuel economy. If you install colder thermostats then your engine will take longer to warm up, creating carbon deposits and more emissions, perhaps fail state DMV inspection (Emmission test failures are listed on CarFax reports - do you need this?).
The key to keeping a healthy engine cool is to give it enough cool fluids, ie. coolant and oil (and some ventilation), and to start the cooling of those fluids before the engine gets too hot.

Q. Should I use radiator hose filters?

A. No. If you change your radiator fluid on a yearly basis then you don't get dirty radiator fluid. Adding filters moves the blockage to another location but certainly doesn't help your engine from overheating. Do you want to protect your engine or your radiator?

Q. My car runs hotter the faster I drive, will your fan system fix this?

A. Absolutely Not. Cars don't need fans when driving above 35mph. If your engine starts getting hotter as you drive faster then your engine or radiator has a serious problem and an electric fan system won't help you.

Check your radiator. Have your engine oil analyzed to determine whether you have engine damage before spending any money on fixing overheating problems. Try titanlab.com for do it yourself oil and fluids analysis services.
----------
Hope it helps,
Wolfgang
v12s.com

 

That is where my 89 always ran. Always. My 85 runs just like yours used to. But I am assuming you mean the line that is immediately above center.

IMO, you would want a short undertray under your engine compartment to change that, but that could mess with your high speed stability, not that I would know.

I really don't think you have any problem. If you have an aftermarket undertray, make sure you have those little scoops that take the heat away from the manifolds, but that is all I would do.

 

What are your actual IR temp readings? (the IR sensor "gun" itself can be, effectively if not perfectly, checked by reading a pan of water at a rolling boil at sea level. And/or a glass of ice water for the other end.)

I'd also check the cap again, they've been known to be bad out of the box and will cause/enable boil-over. They can be tested at your FLAPS.