Land Cruiser Overheating problem

Land Cruiser 75 and 78, Troopy with 1HZ engine is known to have cooling problems. Especially if they have retrofitted turbo. 80 series with 1HZ, on the other hand, does not seem to be as vulnerable. This may indicate that the pointed shape on the front of 78 leads to poor flow conditions for the air. It is possible 80 have larger radiator as it is wider in front.

I have a 2001 78 that with 250,000 km on the odo. A turbo and intercooler was fitted a couple of years ago. See xx about this. This summer we were in the Pyrenees, it was hot, up to 40 centigrades, and after a long climb of over 1000 height meters, I discovered that the engine was boiling when we parked to look at the views. I had experienced before that the engine could get hot so I kept an eye on the temperature gauge, but this showed normal temperature. Still the engine boiled.

Oil temperature, not cooling water temperature.

Back home after the trip, I started to dig a little into how to improve the cooling, and why it could boil while the temperature gauge showed normal. The latter turned out to have a simple explanation. It turns out that the temperature sensor is mounted in the block, in the oil gallery to right of the oil filter. That means it does not measure water temperature, but oil temperature. That is, the water temperature can rise rapidly without the oil temperature following. On some cars, including those with Australia spec, the sensor is mounted in the water outlet after the water pump. A sensor here will measure the water in the hottest place, before it enters the radiator.

Even though my car did not have a sensor here, the mounting hole is there, sealed with a plug. So the first thing I did was buy an extra water temperature gauge with sensor that I mounted in the hole. The hole has M20 X 1.5 threads. This is a standard, and there are sensors that have this dimension, but most have 1/8″ NPT threads. Fortunately, there are adapters to buy. See details about temperature meters and test of these further down.

With a temperature sensor in the water flow, I will be able to follow more to possibly stop before the engine starts to boil. But it would also be nice to be able to avoid this, even at 40 degrees and a lot of ascent. For normal road driving, this is not a problem, even at 40 degrees.

Turn off the AC

The simple solution to avoid overheating is to drive in low gear. High speed cools the engine by increasing the flow of air through the cylinders while the fan draws more air through the radiator. On turbocharged engines, this is especially important to keep the exhaust temperature down. Another trick is to turn off the air conditioning, the AC in long uphills, if you have it. The radiator of the AC is mounted in front of the engine radiator and will heat the air before it hits the radiator when the AC is on.

Reduce weight

My Troopy is rigged for overlanding. With interior, equipment, water and diesel, it is very heavy. So keeping the weight down is important, and it also has a permissible total weight to keep below. The car was equipped with an ARB bullbar with winch. This weighs 100 kg, and to some extent covers the radiator. To get the most efficient cooling, it is important not to have as little as possible mounted in front of the radiator, such as extra light. But also the ARB itself probably creates extra turbulence, and it covers the lower part of the radiator. A standard steel bumper weighs 20 kg, so it is 80 kilos saved by going standard. In addition, this solves the problem that the bumper is not legal in Europe. Kangaroos are also scarce in Europe, so the radiator protection itself is no problem to lose. But the winch? I have been overlanding for over 10 years, and in those years I have only used the winch 3 times. All times to pull out other cars. My car is equipped with lockers at front and rear, and with sand ladders and hi-lift in addition, we will probably manage. In the most desolate areas, you should anyway drive several cars together.

Dirty radiator

When I took off the ARB bar I found the lower part of the AC condenser (radiator) was full of clay. It was not possible to get access here as long as the bar was in place. A thorough use of a high pressure washer removed clay and insects. But be careful with the pressure. Keep the washer 30-50 cm away so as not to warp the cooling fins.

Don’t block air flow

In addition, I moved one horn away from the radiator and onto the side. Doubtful about this gives dramatic results, but easy to implement. The dryer bottle of the AC is also in front of the radiator, but difficult to relocate.

Mosquito net

As the picture shows, the radiator is now covered with a mosquito net in stainless steel. The advantage of this is that the radiator is not clogged by insects. Mud splashes will also be stopped by the mesh, and it is easy to clean. The downside is that it also obstructs the airflow. So this is still at test. If the car still gets too hot I will take it away again to see what significance it has.

Radiator cap

After a bit of googling about the problem, I have a list of other measures against overheating:

Hoses

Replacing radiator hoses. If the hoses have become very soft, they can contract and block the flow of water. This applies to the lower hose where there may be negative pressure.

Fan – Viscous Coupling

Heavy Duty Radiator

There are larger radiators on the market. These are popular especially in Australia. From what I can read it is questionable how much these improves cooling, especially considering the price.

Over fueling

If the pump delivers to much diesel the engine gets hot. This can be a problem if turbo is fitted and fuel turned up to much. Can be avoided with boost compensation.

Summary

Simple measures:

• Keep the speed up.
• Switch off air-conditioning On long slopes.
• Wash the outside of the radiator. Remove insects and manure.
• Remove anything that obstructs airflow through the radiator, such as auxiliary light.
• Install temperature sensor in the cooling water.
• Rinse the radiator and block when changing coolant.
• Change coolant at the right interval to avoid corrosion. 3 years for Toyota red, 5 years for pink.

Major measures:

• Replace radiator cap.
• Replacing radiator hoses.
• Replace viscous coupling or renew silicone
• If retrofitted turbo, not too high charging pressure
• Too much diesel / over fueling. (Black smoke)
• Switch to larger radiator.

After mounting the temperature sensor, I have tested a bit, and the temperature is in the range 80-85 degrees on the highway at 110 km / h. I have tried a bit climbing without the temperature rising. But then with 15 degrees in ambient temperature.

Temperature gauge test and correction

The following is a bit technical, but if you want to test your gauge and if necessary correct the reading you will find the info here.

I bought a cheap gauge and thought it might be a good idea to test the instrument before fitting it. If it is to help prevent overheating it should be accurate.

Since the coolant temperature is up to 100 – 120 degrees, it is at this range that it is important it is displayed correctly. And this is easy to test. Just stick the sensor in a pot of boiling water, and the instrument shold show 100 degrees. My meter showed 110 degrees, so that was a big and unacceptable error.

I could buy a more expensive, and maybe better gauge. But I think most such instruments are quite inaccurate, so I chose to correct what I had.

Such instruments normally use an NTC resistor to measure temperature. This is a resistor that decreases in value the higher the temperature becomes. So when the instrument showed 110 degrees instead of 100 this means I have to increase the resistance value a bit.

In my case, I heated the water to the instrument shown a little over 100 degrees. Then I turned off the heat and waited until the temperature dropped back to 100 degrees on the instrument. It is important to take a short break here because the sensor is encapsulated in a brass lump that takes some time to heat up. When the instrument showed 100 degrees, I connected one wire to the sensor and measured the resistance value with an ohm meter. It showed 158 ohms. Do not remove the sensor from the water when measuring.

Then I heated the water further until it boiled. After boiling for a while, I disconnected the sensor and measured again. Now the resistance was 124 ohms.

But at 100 degrees, boiling water, the sensor should be at 158 ​​ohms, as tested above. To correct this I had to increase the resistance value by 158 – 124 ohms = 34 ohms.

So I simply soldered a resistor of 33 ohms into the wire of the sensor, i.e. in series with the sensor. (34 ohm resistor does not exist). Now the instrument will show correctly in the range around 100 degrees, but be wrong at low temperatures. But that does not matter.

The gauge shows too low a temperature

If the instrument shows too low a temperature, for example 95 degrees in boiling water, this can also be corrected, but it becomes a little more difficult to measure. But it can be done like this:

Heat water and stop at a temperature below boiling point, for example when the instrument shows 80 degrees. In the formula below, it is called T₁. Measure the resistance as explained above. We call it R₈₀ for example 180 ohms.

Then heat the water until it boils. The instrument now shows 95 degrees. In the formula below, it is called R₉₅, for example 165 ohms. T_B is the temperature the gauge shows when water is boiling.

But the instrument should show 100 degrees, so we have to find out what resistance this corresponds to, and we can do that by so-called extrapolation.

The formula for this is:

For each degree the temperature increases, the resistance decreases by: (R₈₀ – R₉₅) / (T_{B –} T₁)

In the example above, this is (180 – 165) / (95 – 80) = 1 ohms / degree.

The instrument showed 95 degrees when it should show 100. To achieve this, the resistance must be reduced by

1 ohms / degree * 5 degrees = 5 ohms

That is, we want the resistance of the instrument to be 165 – 5 = 160 ohms to show 100 degrees.

When reducing the resistance, the resistors must be connected in parallel. The general formula for this is

R_|| = (R₁ * R₂) / (R₁ + R₂) R_|| is the resistance you get by connecting R₁ and R₂ in parallel.

But we are looking for the resistance of the resistor to be connected in parallel to the instrument so the formula must be solved with respect to this.

R₁ = (R_|| * R₂) / (R₂ –R_||) R₁ is the resistor we are going to connect in parallel to the instrument that has resistor R₂

With example values ​​this is:

R₁ = 160 * 165 / (165 – 160) = 5280 ohm. A standard resistor of 5100 ohm (5.1 k) is reasonably close.