Thermostats are a relatively cheap and easy to replace part on an engine. They are designed to help control the temperature of an engine and to minimise wear and tear.
Internal combustion engines work most efficiently when they are running at a warm temperature. While an engine is warming up and before the oil starts flowing there is a lot of wear on the moving internal parts, so it is ideal for the engine to warm up as quickly as possible. This is one reason why when you go to buy a car you do not necessarily want to purchase one from somebody who has just ‘nipped to the shops down the road’ in their car and not used it for any longer journeys. Thankfully the thermostat is there to restrict the flow of coolant to the radiator until the engine has warmed up, which in a typical BMC or Leyland engine will take about 5 minutes. Once the temperature of the thermostat is reached then the thermostat opens and it acts like a valve, it then allows the coolant to flow through the radiator causing cooling of the coolant and therefore cooling of the engine, this helps to keep the engine at its optimum working temperature.
Put simply, a thermostat is a device that reacts to temperature, they react by opening and closing a valve or by turning a switch. A thermostat has two positions, open and closed. Typical tractor thermostats are controlled by wax pellets, that are designed to have a specific melting point. When the wax melts it allows the thermostat to open. By varying the composition of the wax that is used in the thermostat the temperature at which the thermostat opens and closes can be controlled.
What Temperature Do We Want The Termostat to Open and Close?
The temperature at which you want a thermostat to open and close depends on which engine you have, what application the engine is being used in (is it in a tractor, a boat or a stationary pump) and also where you are in the world. The tractors that we sell parts for, Nuffield, Leyland and Marshall tractors, have BMC, Leyland or Perkins engines in them and they are typically designed with thermostats that open and close at 82 oC, but this is not always the case.
A lot of these BMC engines and Leyland engines are fitted in applications other than tractors and many are marinised and fitted in boats. Boat engines of these type are typically fitted with a thermostat which opens and closes at 74 oC. By opening at a lower temperature, the thermostat prevents over heating in the boat.
The 74 oC thermostats are also fitted in the Nuffield M4 engines with the Petrol TVO engines.
We also sell the 74oC thermostats for Nuffield, Leyland and Marshall tractors in hot climates, such as Australia, parts of Africa, Southern Europe and Asia. By opening at a lower temperature, the radiator has a head start to keep the engine cool and stop it overheating.
There was a discussion about fitting 74 oC thermostats to tractors in the UK last summer (the summer of 2022) as it was exceptionally hot compared to our normal climate). Who knows if in the future this may become something to consider.
On the flip side there is an option in the parts book for a thermostat that opens at 88 oC which is designed for cold climates. By opening at this higher temperature, it allows the engine to keep that bit warmer in these colder climates. This would be ideal for colder climates such as Norway, Sweden, Northern North America, and Canada.
You can tell the opening temperature of these tractor thermostats if you look underneath. If you look down the hole underneath you will see the numbers stamped in – 74 oC or 82 oC. The picture below shows where you will find this marking, although you cannot see it in the photo it is down the hole that we are pointing to.
What is a Foot?
Have you ever heard people talk about feet on a thermostat? Well, the foot is the bottom of the thermostat and you can see the difference in the pictures below. The left-hand picture shows a thermostat with part number 13H7508, which is a thermostat with a foot, or a jiggle pin as it is sometimes known, and is fitted to the BMC 2.6,2.8,3.4 & 3.8 engines and the Leyland 4/98 and 6/98 engines. The right-hand picture shows a thermostat without a foot, in this case part number GTS101, which is an 82 oC thermostat which is fitted to the BMC Mini tractor as well as the Leyland 154, Nuffield 4/25 and Marshall 302 tractors.
How Do I Know If My Thermostat is Working?
If your thermostat is not working on your Nuffield or Leyland tractor then it can cause problems for the engine. If the thermostat does not open, then your engine will overheat and it will cause your engine to boil and it will damage your engine. Equally, if the thermostat opens too early, or is stuck open, then your engine will not reach its optimum temperature and the engine will run less efficiently. Cold engines run inefficiently which leads to increased fuel consumption.
You can check your thermostat is working by putting it in boiling water and watching it move when the temperature is reached. We have done a video to show this on our Facebook page – click here for this video on testing your Leyland tractor thermostat. Did you know that we love making videos that make things easier for you. I post these videos on our Facebook page and our You Tube channel. You can follow us on Facebook and subscribe to our You Tube channel for more information.
This video shows that in order to test your thermostat you put it in freshly boiled water. It then shows how the thermostat itself can absorb some of the heat from the freshly boiled water and how this can drop the temperature of the water so that it is below the opening temperature (72 oC in this case). So, you discard this water and pour in fresh hot water and you will be able to see the thermostat open while in the water. Many people when testing thermostats do not change the first lot of water, so they come to the incorrect conclusion that their thermostat is not working. In truth thermostats rarely go wrong.
Not Just a Thermostat, It Is All About The Radiator Too
Your thermostat is only one component in the cooling system of your Nuffield, Leyland or Marshall tractor. The cooling system is made up of the thermostat, the water hoses and the radiator, as well as the coolant itself.
As well as checking that your thermostat is working, it is always good to check that your radiator is not blocked, that your hoses are not perished and that the coolant is topped up and has the correct concentration anti-freeze in it. These all work as one system to ensure that your engine is working at the correct temperature.
Thermostats available for Nuffield, Leyland and Marshall tractors with BMC and Leyland engines at Tractor Spare Parts Ltd.
