moinhaider

Hi there,

I recently had the alternator, water pump, timing belt, auto tensioner and pulleys replaced on my 1995 Toyota Celsior. The shop doing the work also changed out the engine fan hydraulic fluid. Ever since everything was put back together there is a noticeable increase in engine fan noise which makes the car sound almost like a truck or SUV. The engine fan is a hydraulic OEM setup. The mechanic said since they've changed out the engine fan fluid it's moving much more freely hence the increased noise. However to me it still seems unacceptable and unlike what this car should sound like. Any thoughts from fellow LS400/Celsior enthusiasts as to what could be the cause of the increased noise? Also is there anyway to adjust the hydraulic pressure in the engine fan system to reduce the speed with which the fan turns? Cheers!

Yamae

I worry that the mechanic made some mistake. One thing to consider is that the water temperature sensor attached to the radiator is not working right or the harness for it is short circuited or improperly connected.

The hydraulic unit is controlled by the ECU getting the resistance value from the temperature sensor. Smaller the value, faster the fan speed. The high fan speed is often caused by the too small resistance of the sensor or it's wire is grounded.

Other than the sensor related issue, there is a possibility that the valve attached to the hydraulic unit is fully open. This is caused by the cold side of the wire from the valve is grounded.

The important first step would to check the harness/wire for the sensor and the valve, I think. It would be best to use a multimeter to check the continuity.

moinhaider

Thanks for the prompt response Yamae. I will bring this up with the workshop manager this week. Letting you know the feedback.

moinhaider

So we checked all connections and resistance values and everything checked out fine with no warning lights on the dash. Voltage for the hydraulic pump was cycling between 2.5V-12.5V. For the time being we're trying to use a lower weight oil with the logic that it would create less pressure and hence the fan would spin slower but so far not much has changed.
The shop is recommending replacing the engine fan clutch assembly & hydraulic pump unit saying that the internals could be functioning below par as the car is now 23 years old.
Any suggestions....?

Yamae

There isn't any clutch. It seems to me that the mechanic and you don't know how the fan system works.
What was the resistance value of the temperature sensor when cold and after warmed up?

moinhaider

For sure we are confused as to how the system works!

Resistance values as follows:-

4.08 ohms cold
0.88 ohms warm

Thanks for your valuable and prompt feedback

Yamae

According to the specification in the JDM service manual, the resistance of the temperature sensor for the fan is specified 1.53 ± 0.05 kohms @ 80 degrees C.
The value you measured was strange even if it's 0.88 kohms.

moinhaider

Can the coolant temperature sensor go bad with age? Hence the inaccurate resistance values. What do you suggest?

Yamae

Below is from the FAQ and is about another temperature sensor but you'd better to know that many people became happy after changing the coolant temperature sensor for the ECU.
All LS400 owners with bad gas mileage READ THIS! (ECT-coolant temp sensor discussion)

As far as I have experienced, a thermistor increases the resistance value quickly when used in high humidity circumstances. Your's shows too small resistance and I just wonder why?

moinhaider

Not sure why the resistance is low... I've read elsewhere that the cooling system needs to be bled of air if you've replaced the coolant during water pump replacement... Do you think bleeding the system would help?

Yamae

Even the air is trapped, still the fan doesn't run too fast when the engine is cold started. Why do you jump to other issue while the too low resistance problem is there and not touched? At first, I'd simply use a variable resistor to check the control circuit is properly functioning or not.

moinhaider

Dear Yamae,

I changed the engine coolant temperature sensor for a new one. The old one was corroded and rusty, broke off on the way out. However the engine fan noise is still present.

Do you have any further suggestion?

Thanks & regards.

YODAONE

Increased fan noise appeared after service...

Go to a different shop to determine the issue and request written estimate.

If something disturbed during service, then you can present those findings to the first mechanic.

400fanboy

I thought the hydraulic fan clutch wasn't really serviceable, the metal spring and fluid inside are lifetime parts and you just swap out the whole unit if they break.

moinhaider

Hi Yamae,

Would you mind explaining how to check the circuit with variable resistor?

Thanks!