928autobahndreamer

I had a curious thing happen on an extended aggressive drive this past weekend. The first half of the drive was great with temperatures never running more than a few needle breadths above the lower (middle) white line.

Then, I began to notice the needle starting to creep up to the upper white line, especially when slowing down for towns or brief bursts of acceleration. I figured that things were just getting "heat soaked" and didn't worry about it too much as the needle never went above the upper white line.

However, the next few days have shown the car heating up quicker than normal and running hotter. Never above the upper white line, but I haven't run as aggressively because I don't want to get things into the overheating range.

Any thoughts? Is it possible that my thermostat got stuck on this last run and is interfering with cooling? What else should I be checking.
Prior to this weekend, the car ran just above the lower white line in normal driving. As far as I know the thermostat has never been changed. Is it just time to swap out with a new along with the seals?

Thanks,
Steve

mark kibort

check for air in the system, slipping or noisy water pump, or the seal on the back side of the t-stat that mounts in the block

david928

I'm troubleshooting my cooling system now because of a similar problem. My engine heats up when stuck in traffic. So here's what I recommend checking in the following order (least expensive items first):

1. Thermostat (like Mark said)
2. Radiator cooling sensor (lower front on driver's side). This could keep the fans from coming on. Note that this sensor is different from the cooling sender that drives the temp gauge, and the Temp II sender, and the intake manifold temp switch.
3. Cooling system control box (interior next to passenger door sill behind a cover). You can check this by turning on the A/C. The radiator cooling fans should come on. There is a test procedure for this box in the WSM.

Good luck
David

Leon Speed

What about the reservoir cap, is it in good shape?

Charley B

It sounds like you may be running on only one fan. Either intermittently or all the time.

Mrmerlin

do you have the cowl flaps installed and hooked up? Is it possible that they are closing while you drive?. If you have them drive it till the temps go up then pull over with the engine running and check them, if they are closed you can open them manually and then pull the fuse

928autobahndreamer

Thanks for the replys. The fans definately come on, but I have not checked to see if both do. Did not even think of that as a possibility. I will check to see if the fans kick on when the AC is turned on. I am a little suspicious as I don't think I have noticed this.

Will also check the cowl flaps, to make sure they are functioning as well. Thanks everyone.

928autobahndreamer

I had changed the coolant in early spring and did my best to burp the system while adding, but is there another method to check for air in the system?

I wouldn't know how air would get introduced into the system later, as things were running pretty cool all summer.

As far as a noisy water pump, what kind of noises should I be listening for? I don't hear any obvious squeeling, or cavitating in the area of the water pump. Do I need to pull the timing belt covers and look for anything?

Again, I really appreciate everyones input.

Steve

blitz928

I'd 2nd that, Be sure your fans are both operating properly.

SharkSkin

Good suggestions above. Some other things to consider:

Park level or, if on a slope park with the reservoir upslope. Check the water level. It should be within an inch or so of the top of the reservoir. Mine usually runs ~1/2" from the bottom of the filler neck.

You should check and see if the car is actually getting hot -- an IR gun on the t-stat housing/upper hose will help evaluate this. The gauge sender could be going bad. If it happened after maintenance instead of during a drive I might speculate that the electrical connection in the gauge circuit may have improved recently, perhaps from having been wiggled.

Does your car have the cooling flaps? Are they working properly or fixed open?

How's your T-Belt tension? Check it, don't rely on the warning light.

HTH

Mrmerlin

to test the fans simply turn on the AC both fans should run, the way to get the air out of a 928 coolant system is to run the motor with the coolant bottle cap off till the fans come on and the heater on full then install the cap and take a 5 mile drive park the car and let it cool when its cool top up as necessary fill the coolant bottle to the seam or halfway

Charley B

Really! I have always run mine just above the center line of the resevoir. Somewhere I got the idea that was the fill line. Hmmm, that may explain a few things.

Jim M.

The thermostat sets the minimum temp of the engine after warm-up. Once open; heat transfers to the radiator, subject to water and airflow. If flow is inadequate and the thermostat is fully open, the problem is the water pump, or radiator restrictions. Check radiator first, they’re more common, easier and cheaper to fix.

Airflow also varies, at high temp, at idle, the fans provide airflow. That setting comes from the temp switch and AC operation for the electric fan on pre S4’s. On S4/GT/GTS’s, a variable speed controller reads coolant temp, checks the AC system, and tries to hold 195°F by varying fan speed. This all interacts so a car that overheats at low speeds but is OK at high speed often has airflow problems. Due to a electric fan, or thermo switch, or both. A car that overheats at high speed often has water flow problems, usually a restricted radiator. A car that overheats right after startup has water problems, a thermostat stuck shut, an inop water pump, a plugged radiator, or no coolant.

S4/GTs have the additional temp control function of the flaps that try to maintain 195°F. In proper operation, there are 3 flap positions, based on engine temp and AC system pressure. Fuse # 23 powers the system.

Lower temp thermostats let the engine run cooler, if there’s radiator capacity. If your car overheats, a thermostat only helps if it was stuck or plugged and is restricting coolant flow. When the thermostat opens, it expands backwards, against a gasket P/N 928.106.163.00 behind the thermostat, closing the passage and forcing the water through the radiator. The gasket deteriorates and the thermostat can’t completely close the passage, so some of the coolant recycles through the engine, getting even hotter.

A low-temp thermostat doesn't flow more; it flows sooner. Fan operation must be coordinated with the thermostat to stay cool. Match the thermostat temp to the fan switch, so the fan doesn't run before the thermostat opens. S4/GT’s are poor candidates for low-temp thermostats, because the flaps stay closed if the coolant temp is low, and the AC is off until 195°F.

Flaps fully open are not flat to the airflow; there is some angle flowing air UP. Start the car with a cold engine; the flaps should close. The electric fans operate based on coolant temp and freon pressure. If the AC is off, the temp will hover within the fans' control range when driven slowly, dropping to the thermostat's setting when the car is moving fast enough to not need the fans. Temp will swing from thermostat temp at higher speeds up to fan controller temp when going slow. In slow traffic with just fan air and low water flow, it's normal to see the temp come up a little with AC. But, up towards the red area isn’t normal.

Flush the debris out that gets packed in the condenser and radiator, blocking airflow, with a hose from the front, but don’t bend the fins. Redline Water Wetter made it almost 3 needle widths cooler. I've had good results running the Prestone cooling system cleaner through the engine. Follow the directions about removing all the old coolant first. Drain and flush the cleaner and water mixture out of the engine, remember to pull the block plugs to get all the sand, rocks and other debris out of the water galleys. Install new seal washers and anti-seize on the block plugs. Torque to 25 ft/lbs., be careful not to strip the block. Use just enough Dex-Cool for the freeze protection needed, use distilled water to reduce mineral scaling.

Remove the water temp sensor located in the cooling crossover manifold at the front of the engine. Fill the system from here and reinstall the sensor. Remove the radiator end of the vent hose until you get a small stream. This is the highest point in the coolant system, and will get rid of the air bubble. Start the car and watch the level.

SharkSkin

Well, I can't see through the side of my reservoir anymore, and I never did find "the mark" so the first time I drained & refilled my coolant I just filled 'er up to the top. Any excess water goes out the overflow when hot. After a few hard runs the water level stopped receding, and I just eyeball it to that level now.

I think the airspace is intended to give room for expansion in the event the cap doesn't release, but since I put a new cap on at the same time I wasn't worried about that.

If the water level is down around the seam I get gurgling in the system. I'd rather risk incurring the wrath of the granola-munchers by spilling a couple ounces of coolant than have air in the system.

jon928se

Check that the radiator shroud? is securely fastened - not the cooling flaps - in front of that examine through the grille in the front pu. check they can't move. most common failure is the lower part comes undone from the back of the pu and flaps up when moving blocking 50% of the airflow to the rad.