Thread: Causes of engine running hot

Originally Posted by pfillery

My series 3 has a 186 but this question should apply to any engine so I put it in technical chatter in the hope of getting a wider range of answers.

I recently changed a rusted out water pump, fitted a new one. The radiator is a 4 core standard one from a 6cyl land rover running a thermostat fan mounted in front of it. The engine seems excessively hot, I'm not sure how hot but it seems to feel like a lot of heat radiating off the engine when you open the bonnet. More than would be expected according to someone who had a look yesterday. With the radiator cap off the water had movement once the engine warms up so the thermostat seems to be ok, the radiator cores look ok and I ran a cleaning flush through it before filling the coolant after I changed the pump. Any ideas?

And on another note, what is the exact purpose of the heater (hot water) lines that run to the underside of the inlet manifold? Are they to cool the inlet (cause I don't think that really works) or are they to warm the inlet in the winter? Seems counterproductive to have hot water running under the carby, fuel burns better when it is colder.

First question - is it really running hot? A decent temperature gauge might give the answer - "the engine seems excessively hot" doesn't really give a lot of information.

If it is relying on an electric fan to move air through the radiator, this in itswelf may cause the engine to appear to be a bit warm, because where an engine driven fan is running whenever the engine is, the thermostatic fan will not be, so the surface of the engine will be hotter when running or just after running, if the fan was off. And it is unlikely that the electric fan moves as much air as did the engine driven fan. But this should not result in overheating except in extreme conditions when driving slowly.

Causes for an engine running hot, to answer the original question.

Coolant leak
Coolant not circulating due to blockage, thermostat, radiator core or hoses
Airflow through radiator restricted, usually by insects, dirt, grass seeds
Slipping fan/pump belt
For thermostatically controlled fan, thermostatic switch wrongly installed or faulty or wrong temperature, or electrical fault, or fan inadequate.
Mixture too weak
Spark timing retarded
low oil of oil not circulating properly
Incorrect oil


The water heating for the intake manifold is to prevent carburetter icing. As fuel is vapourised in the carburetter latent heat of vapourisation causes the temperature of the mixture to drop. If conditions are such that temperature drops below freezing, and the carburetter and manifold drop below freezing as a result, when there is significant humidity in the air, ice will build up on the interior surfaces of the manifold and/or carburetter. This will rapidly cause loss of power and even complete stoppage, and is very difficult to diagnose, as the ice will be melted by the time trouble shooting starts.

Temperature range where it can happen is from about -5 to 25C. As a result, all modern (post 1920s) carburetter engines have some form of heating. With fuel injection at the ports, there is usually enough heat that no special provision is necessary.

John

So, JD, does that mean that in Qld where the temp never seems to drop below 100 degrees in the shade that I should be able to bypass that heater line to the manifold?

I'm wondering if the layout of those lines is important too? Looking at the underbonnet of any old holden, the position of those lines and how they run is different to the landy, ie the 2 outlets near the water pump go to the heater core and there are 2 others for the manifold - on a holden they run differently as one pair of lines is crossed over.

Whe I describe it as running a bit hot, I'm going by what someone told me who seemed to know a bit about them.

Stop guessing and try measuring how hot it gets. Your face is not a temperature gauge.


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Originally Posted by pfillery

So, JD, does that mean that in Qld where the temp never seems to drop below 100 degrees in the shade that I should be able to bypass that heater line to the manifold?

You can bypass these if you wish, I 'll go bit higher with temps than JD and have witnesed Carby ice with temps above 30 if the humidity is right.
Its your call and I suppose you have to decide what impact the motor stopping (albeit under some conditions more than others) will have on your every day use. The manufacturers obviously had the issue to fit the hoses in the first instance. I dont think the 186 will really deliver any real gains in economy or power for the removal of those hoses. But thats just my thoughts.

cheers

I think the other reason we have heated manifolds is to bring the engine to operating temperature more quickly and to keep the whole engine within this range for the sake of efficiency. This is why we have a thermostat.

If you look at an engine like the TD5 it has the fuel cooler on it (return to tank).Why would we have pretty hot fuel running to our injectors? Is it more efficient?
It is "cooled" and also heated by the engine coolant.

I think an engine is designed to be operated in many different environments with a Landy this would be over a range from -20c-50c i would say.
Yes most engines seem very hot, my P38 runs at 90c + thats just normal.
I have had concerns at times and thought she is hot now and put an infrared thermometer on the engine and it is still only at 95c.

Look at wrapping your exhaust manifold to get rid of heat under the bonnet you will also increase power by maintaining higher exhaust temps due to the escaping gas having a lower density and this allows it to flow faster.

Sure cooler air into an engine makes more power think of a cool night or intercoolers and we see more power.

I guess modern engines are all about consistent reliable running.