ebs

Hi, just recently my 928 has started to run quite hot. It is summer, but the weather has been warm for months, so that should not have an impact. The temp guage is going almost all way to the last white line. That said I am suspicious of the guage, as there is a bit of flicking of the needle, for example when I tap on the instrument's glass or even turn on the head lights the needle does shift around a bit. I will also mention that I generally drive it quite gently and the air conditioning being on or off (I do have an a'c lea though) seems to make no difference to the guage. A few other issues I should mention:

1) I am using Castrol Magnatec oil 10w/40, and the car is full on the dipstick.
2) the air fuel mixture is about perfect - checked recently
3) I always use premium unleaded and there is no engine knock/pinging
4) the raditaor appears to be in good condition visually as do the main pipes around it. The car uses very little or no water/coolant (ie, I use Valvoline coolant). The main pipes get hot, but not hotter than say my brothers 1989 Toyota Supra (3 liter) Turbo. The radiator is full and coolant changed within the last year (around 3000 miles ago).
5) the condenser fan rarely comes on in the car, and even with the temp guage soaring it has not come on. I have see it on before though so it should work. Hence my reason for suspecting a faulty guage.
6) Oil pressure is fine. Around 2.5 when engine is warm and on 5 when cold. If it was water temp was that hot I'd expect the oil pressure to be even lower.
7) virtually nothing out the exhuast, so unlikely to be a head gasket?

So what can I do about this? Change the radiator cap? Should I remove or check the thermostat? Can I check the guage or clean the sender unit or something? How would I do that?

Sorry for the long post. All assistance very much appreciated to ensure my Shark is healthy.

Drewster67

Maybe the radiator needs to be recored?.

Doug Hillary

Hi,
ebs - are you a member of Landsharkoz?

What part of OZ do you live in?

This subject comes up regularly with all the relevant and irrelevant information being reprocessed time and again. Check search on here and all you need to know will be revealed

Firstly you need to ascertain if the car is "really" overheating and the search results will assist in this process!!!

Regards

ebs

Thanks guys. My seach did not reveal much, thats why I posted here. Doug I am in WA. As my car is closer to being US spec than anything else, I find I get the best info and help here, but Landhsarkoz are very good too.

Would anyone say its water pump related? I would guess not as its not using much (if any) water.

the flyin' scotsman

ebs...........a cars cooling system is relatively simplistic...........insure the water/antifreeze is correct mix/ correct level and at newer than 2yrs. Check all hoses and any exterior rad blockage. Does your car have the 'flaps' in front of the rad?........if so ensure they're opening when they should. The water pump is driven off of the crank via the camshaft timing belt.........when was the last time the belt was tension checked and/or replaced? By your discreption it sounds as if the issue is not severe if at all.............check all of the above before assuming the pump is the culprit..........its the most expensive and labour intensive repair!

Nicole

If my 928 was running hot without any obvious reason, i'd be worried about a water pump failure. Any noises from that area?

Drmark

See this post from cfc928gt (search under oil pressure warning - ? false alarm for whole thread). I know your hot oil pressure is fine but he thinks this is a common problem with 928s and a fix that is missed by most people with hot running cars with no obvious reason.

"The problem is your oil thermostat. I brought this up in Wichita at the 928OCIC tech session last year. I think this is becoming a common problem that affects not only low/no oil pressure when starting a hot engine but I also think this is a contributing factor to S4/GTs that run hot (touching the red) since this seems to have some influence on oil flow to the radiator. Since the oil thermostat is a bi-metal piece it will fail over time just like a coolant thermostat. The fix is simple and cheap. Part # is 928.107.172.02, I paid $30.39 from one of the big three last year. No one seems to know about this, in fact the 'big three' listed the part as generic and put the part number in the footnote section. Not only did it fix my oil pressure problem but my GT is no longer running up to the red mark on really hot days. I'd been trying to solve the cooling problem for three years as well as the oil pressure problem...simple fix. Remove your oil filter so you have room, remove the oil pressure sending unit and pull out the thermostat. Installation is the reverse"

ebs

Thanks for your replies.

As there is no water usage I don't think the pump is the issue and I do not hear noise from that area. What kind of noise would I hear? The cam belt was done a year ago (about 3000 miles ago) when I bought it - car had no maintenance history but had low mileage on the clock (around 70,000 km or 44000 miles), but had been standing for some time unused. Cam belt was checked again shortly after being changed and should be fine. Water pump was not renewed as P mechanic said it was fine then.

I showed the car to a a friend today who is a mechanic (no a P car mechanic though) and he said all looked fine, and both main pipes to radiator. The only issue he suggested was the main fan, which he said had almost no resistance to it when he spun it with the engine off. He thought this should be further investigated as it may not be doing its job as its just spinning but not cooling. I couldn't understand how that works -t me it either spins (= good) or it doesn't (= bad). What do you think? Should it have resistance?

The temp was actually running in the middle today, which I'd think is normal for a 35 C (95 F) degree day. Condenser fan came on when I put a/c on and stayed on when I switched it off. I assume thats normal.

Can someone please give me an idea how to locate and clean the temperature sender unit please.

Nicole

The fan in your car is not electric - it has a viscous coupler. When the engine is cold, the coupler is disengaged, letting the fan spin freely without resistence (kind of like when you press the lutch on a manual transmission car and turn the wheels). When the engine is hot and needs the cooling, the fan shouls turn - have you seen it turn?

There have been reports of viscous couplers going bad when cars were not in use for prolonged times. I'm sure some of the owners of the pre-S4 models can give you more insigt on this - or try searching this message board for past discussions on the fan and coupler.

Hope you can sort it out!

ebs

Thanks for your post Nicole

The main fan is always turning when the engine is running. The condenser fan comes on from time to time - heat/pressure based I guess.

What you are saying though is that the main fan should be able to spin freely when pushed by hand (with the engine off) and there should be no resistance?

Garth S

Ebs,
Viscous coupling fans are silicone fluid filled clutches that will slip with little resistance when cold - and as they heat up, the resistance to turn increases: this allows the fan to consume more power/draw more air as the rad exit air temp increases. Spin the fan when cold - and repeat when hot ( engine off ): there should be an increased resistance. It does not 'lock-up' like a transmission clutch.
There is a fix for that should it be a problen (link to Nichols Tips IIRC) where one refills the fluid with an available Toyota juice.
Anyway, #1 is to determine if the coolant is really hot - for if you have flickering gauges, poor electrical grounds within the pod cluster or at the sensor are more likely. If overheating, both main rad hoses will tell you so. If you can feel a temp differential left to right - and can get your hands on the pump discharge hose without jumping, you are not overheating. The scientific way is to get/beg/borrow an infrared gun, and measure the temps.
BTW, the 2.5 bar oil pressure quoted for a warm eng is at idle?? - At >2500 rpm, the warn/hot pressure would be ~5 bar.

Check the fan clutch first ...

WallyP

ebs,

As has been said over and over - first, determine if you really have an overheating problem. As a general rule, an overheated engine feels hotter than normal, and smells hotter than normal.

You have three indicators that show when the engine is overheating: the temp gauge and the overheat warning light, both of which work from the coolant temp sending unit, and the aux electric fan, which works from a switch in the lower front of the left radiator tank. It sounds as if only one of the three are telling you that the engine is overheating.

That, along with the fact that the gauge is dancing around, and that the engine apparently doesn't feel or act hotter than usual, certainly makes it seem as if the problem is a faulty electrical connection on the temp gauge.

Here in the States, Sears now sells an infrared temp gun for $50 - a marvelous toy that can be very helpful in cases like this. Perhaps you can find some type of thermometer that can help you determine for certain that the engine is not over the normal temp.

I developed the clutch refill procedure for the 928 - here is a write-up on the procedure. Be sure to read all the way thru it, as there were some good suggestions near the end.

http://www.nichols.nu/tip482.htm

ebs

Thanks for all of your posts. I can touch both main rad hoses, and yes they are pretty damn hot, which at last shows there is not a blockage as they are a similar temp. How hot is too hot though? Lets just say I can't hold on to them for long at all.

The 2.5 bar oil pressure is at idle.

Where can I find the sensor or sender unit for the temp guage please?

WallyP

Top center of the engine, on the intake, under the crossbar.

For most people, 140 deg F is about as hot as they can hold for more than a second or two. The normal running temp of the 928 engine is too hot to touch comfortably at all, but normally won't blister skin if you touch it dry.

A thermometer is a better idea!

Randy V

What Wally said!

Plus, there have been numerous instances of the plastic water pump impeller failing to spin on its bearing shaft, resulting in loss of coolant flow and thus overheating. The impeller failure does not cause a leak, and is not revealed by an exterior visual inspection.