nick_968

Engine is a 3.0 turbo in a 968 water pump is new. I have upgraded the radiator to all ally with a front mount intercooler which is attached. Before the rad upgrade my water temps would only drop when the fan kicked in (I had a 951 IC mounted right in front of the airflow and the rad just wasnt getting the air). Now the motorway driving is fine, the water temps stay halfway or below and no probs there. Its the lower speed driving even up to 40 to 50 mph that is a problem. I would expect these type of problems only in stop go traffic where it is acceptable for the fans to kick in an out all the time as the temp goes from the second white mark to the third. It just seems to be running that little bit too hot, especially now I have upgraded the radiator I was expecting cooler round town temps. The radiator itself is very high quality 4 core item so I can rule that out. I have bled the system thoughroughly as well. I know I can solve the problem with a lower temp fan switch but this seems to me more of a band aid. I need to understand more about lower temp thermostats. Some threads I have read say they only slow down the warm up time and once open they dont make any difference. Other threads say they will keep the water in the radiator longer, allowing the radiator to exhange more heat....and therefore reducing overall running temps. My understanding was the first one, that once they are open that is it and therefor will not help my problem.....is my only solution working on the airflow through the rad and ultimately if I cant get improvements, a lower temp fan switch?

Also is the temp sender for the dash independant to the fan switch, i.e. one reads and one operates the fans, or does the fan switch take its readin from the temp sender for the dash? If they are seperate then the dash will confirm the fan is kicking in at the right temps? right?

Techno Duck

There is a seperate temp sender and fan switch. The dash gauge takes its reading right at the top of the engine block, next to the DME temp sensor (which is located right at the coolant outlet).

Im not 100% sure about the fan switch. The fans will kick on at lower temperatures, thus the temperature reading of the gauge shouldnt go as high. I think the misconception is that if the car is overheating a lower temp fan switch will help. As for the thermostat, i was also under the impression that its primary purpose is to help the engine get up to operating temperature more quickly.

Trucho-951

The only problem I see with using a lower temp fan switch is that the fans will be running most of the time, thus, the fan motors will wear out faster and will shorten their life.

ELLSSUU

I can tell you that I run a lower temp fan switch and my fans do run quite often. Not familiar with weather in the UK but in SE Louisiana it gets jungle hot. After my recent rebuild I've noticed that my engine runs considerably cooler i.e. near the second white line (the first being drop dead bottom). When the temp gets just a tad over the white line the fans kick on and cool it back down.

89951DREAMER

Also keep in mind that the DME will run the engine a little richer due to the fact that the engine is not in it's normal operating temp range. The DME will think the engine is not warm enough.

Trucho-951

Nick,
To think this problem through systematically, and come up with an engineered solution, I’d recommend starting with an energy balance around the car’s cooling system. I’ve written a few lines below to illustrate in very simple terms what some options might entail…

Energy balance:

Heat in = Heat out

Mass Airflow into radiator * T1 + Heat generated by engine = Mass Airflow out of radiator * T2

A*T1 + Qe = A*T2 ----------equation #1 (very simplified energy balance)

Qe = A*(T2-T1) -------------equation #2 (a little algebra to rework eq.1 into a more useful form)

Everything is fine as long as engine heat, Q-engine, is equal to or less than the term on the left hand of the equation: A*(T2-T1).

Mathematically, what this tells us is that if Q-engine goes up, in order to keep the engine from overheating, one must do either of the following:

1) increase, A, the airflow through the radiator,
2) increase, T2, the air temperature of air coming out the radiator, usually involves greater heat exchanging surface area (i.e. larger radiator),
3) decrease, T1, the ambient temp. (drive in colder weather), or
4) decrease, Q-engine, (limit engine output, drive like a gramma, install a smaller engine, or limit engine heat by some other means that means less heat load to the radiator)


Now #4 above is an interesting one. Here is a thought, I would say that using louvered hood fits into that category of making the radiator workload much easier. Perhaps you could use a summer hood heavily louvered to vent a lot of the engine heat to the ambient so as to lessen the heat load to the radiator at low vehicle speeds. Then during the winter you can switch back to your regular non-louvered hood to keep the rain out of the engine compartment.

Good luck.

Ski

Nick, what thermostat are you running at present? Did you put any Redline Water Wetter in the system and whats the ratio of water to coolant? The 3.0L blocks have a several mm less depth in the area around the cylinders than the 2.5 blocks do.

What do you have for oil cooling? Did you install the oil baffle plates under the cylinder bores...or should I say oil blocking plates - I've heard varying opinions on those, so I think I'm going to leave those out of my new engine.

The thermal switch in the radiator signals the fans, the first one anyway as I understand it. I've also heard about a batch of bad thermostats from Tom Charlesworth, that people have been reporting when he travels for/with the technical committee. It seems that some from China made it over here for several import brands, just something he sent me an email on. good luck

jerome951

You can always wire a switch to control the fans manually. I've got 2 switches in my car (using the foglight switch location), 1 controlling the low speed fan, the other controlling the high-speed. Not that hard to do.