removing the thermostat

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dogan124

Member
Joined
Jan 24, 2005
Messages
42
Location
Turkey-Ankara
Car
1991 w124 300td (estate) & 1988 Golf II TD
Next month merc will be towing our heavy caravan while it is already loaded by family and packs. It is a well kept w 124 300 D estate AT.

I know on day time the temp indicator will sit slightly over 100 degrees line even on flat roads. Attempting AC or driving on hills will rise it to 110. (Cooling system is renewed other than coolant pump).

Can I expect a better cooling if thermostat is removed. Couple of times I had to start cabin heating to assist the radiator which definetaly helps.
I need some "cooler" methods to increase the cooling efficiency.

Any opinion?

Cheers.
 
Are you sure your radiator is not choked and all your cooling fans are working. Normally 2 aircon electric fans in front of the radiator plus a viscous coupled fan on the engine. Sometimes these v/couplings can fail or the bimetal strip actuator pin seizes or gets covered by road dirt. The coupling has to "see" the air temperature after its passed thro the radiator to operate correctly. The other thing you can do is to install a separate oil cooler instead of using the heat exchanger coil in the radiator. This effectively increases your radiator cooling area which is what you are doing when you use the interior heater.
 
Definitely don't remove the thermostat, not only does it open up the radiator to the coolant it also channels the flow. If you remove the stat then you could see a nice cold engine as the radiator coolant is cold but if extremely hot water is circulating mainly the engine you will overheat without knowing.

Easy things first, run the proper reccomended mix of coolant, plain water can cause cavitation and give less cooling.

Make sure the radiator itself is free of debris, crud etc, give it a good wash with a hose with the engine running.

Check your level, anywhere between minimum and maximum is fine, carry some premixed top up coolant with you.

Fit a new radiator cap (Mine is a pressure release cap, I presume yours is aswell?) as these can bleed pressure off when old or the rubber may not seal correctly. Less pressure in the system means a lower boiling point.

Make sure it is actually running as hot as your gauge says, use a thermometor to check while it's idling (Remove the cap before starting, not after it gets warm or you could get a face full of coolant) and see if it roughly matches what your dash gauge says.

Check your viscous fan is working using the tried and tested rolled up magazine method. Get the engine up to temperature, with the bonnet open using a rolled up magazine, try and stop the fan from turning. Make sure the fan is spinning away from you before doing this. If you aren't 100% confident in doing this, then don't. Mainly as i'd feel bad if you got a face full of heat magazine haha. If you can stop the fan and the engine is hot, you may need a new viscous fan clutch.

I may be incorrect but your engine shouldn't really run that hot at all, has it been maintained with genuine parts? I see just under 90°C on a cruise, below 90°C on a fast cruise in my 500E, when sat in traffic it wont go above 98°C. I've had it at 110°C once after a very hard drive in Italy and literally pulling into a massive traffic jam in april, 5 minutes later it had recovered to 98°C and all with the aircon running.

Dave!
 
Some good points above!

If you need a new radiator go to a radiator specialist and ask for a wide core radiator which will help in cooling, these are used on plant vehicles that run hot.

Ideally it should run at 90 c so your thermostat may be sticking, but check that fan as above..
 
Good point on the radiator/expansion tank cap.:rock:
 
OP says
Cooling system is renewed other than coolant pump
 
I did all the checks described except the accuracy of the temperature gauge. Radiator is new as the largest available size, viscous caupling and thermostat is changed by proper units. I thing the reason is that I'm quite on the towing limits while the temp is around 35 degrees.

The temp indicator normaly (not towing)is abit below 100 (the level line between 80 and 120). It doesn't change much on highway even with AC. In trafic jams It goes up a bit without AC and more with AC. So I assume it is normal.

I thought thermostat causes a kind of restriction even while open due to its geometry. Hence removing will let the coolent flow faster. This should result in a better cooling. I should agree a too cold engine is not a prefered case but actually I don't expect the thermostat would ever be closed after the first five minutes of summer drive on tow.

The other thing you can do is to install a separate oil cooler instead of using the heat exchanger coil in the radiator. This effectively increases your radiator cooling area which is what you are doing when you use the interior heater.

Do you mean AT oil or engine oil ?

Thanks,

Dogan
 
The other thing you can do is to install a separate oil cooler instead of using the heat exchanger coil in the radiator. This effectively increases your radiator cooling area which is what you are doing when you use the interior heater.

Do you mean AT oil or engine oil ?

Thanks,

Dogan

Sorry I meant an auto transmission fluid cooler. This relieves the radiator of cooling the transmission fluid in addition to the engine.
 
Two points;
What's wrong with the engine going upto 110c as long as it doesn't go higher and for the best cooling flush the system with a caustic flush, then fill it with a coolant with additional wetting agent such as Comma Coldstream.
This allows quicker heat soak into the water and back out again so results in a cooler engine.
 
Two points;
What's wrong with the engine going upto 110c as long as it doesn't go higher


I feel good while it keeps at 110 (by the fan in action though the AC is off). But it tried beyond for couple of times on hilly roads, hopefully, the internal heater was there to help.
 
I found the problem was the viscous coupling. It had been changed just about 5000 km ago (less than 2 years) but failed somehow.

The private garrage suggested the coupling of gasoline version for better cooling. I was not expecting any difference but I should say it was the most relaxing tow I ever did in terms of cooling stress. The gauge was almost fixed below 100 line.

It is like working all the time from cool to hot and has a noticable whistle but I will not change it until towing season ends.

Cheers
 
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Excellent news, a properly operating cooling system on one of these should see you at below 100 unless in extreme conditions.

Dave!
 
Excellent news, a properly operating cooling system on one of these should see you at below 100 unless in extreme conditions.

Dave!

Towing a caravan over 1600 kg, at 35 degrees...Yes, I think extreme...
 

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