CNG and Higher Water Temperatures

<...Pls advise how to bring down the water temperature....>

Increase the cooling ventilation.

Natural gas and Propane under combustion gives off more of it energy to heat then gasoline. You could try to correct it by a change in thermostats. Been a while but most cars have thermostats set to regulate temperature to about 180° F. Where forklifts converted to Propane where changed to a 160° F thermostat. You may also want to check the fuel mixture settings running too rich will also increase temperature.

You may also want to check your cooling system. The change in fuels could have made apparent a problem that was about to happen any way if you continued using gasoline.

I agree with the TCMTECH above. You need proper spark advance of perhaps 5 to 10 degrees with CNG relative to gasoline (petrol). Retarded spark leads to high exhaust temperature and high heat load to the water jacket from your exhaust port. If this is occurring, high exhaust temperatures can also increase your risk of valve recession or damage.

Good CNG systems (low restriction) only cause a 10% loss at the flywheel. This is documented by OEM approved systems. The 10% loss is due to ~10% extra displacement of the air by CNG relative to gasoline.

The usual reason for temperature increase (assuming your thermostat is working correctly) is that the engine timing is too far advanced for the new fuel. eg. the new fuel is burning quicker (too soon). You will need to reduce the advance (retard) the ignition to allow the new fuel to burn later......

Seeing a temperature change as you have implies that the ignition is far, far too advanced.......and likely to cause damage as well.

Think of retarding at least 10° as a start......

Most modern engines have a special sensor to "hear" when an engine is too far advanced and to retard the engine automatically. yours appears to either be missing, or it never had one or not working.....

Someone else thought that your engine might be already too retarded, I completely disagree with that personally.....as a retarded engine usually does not overheat....

But retarded bosses and managers overheat all the time!

I had not thought about the timing being over advanced though. Its possible but without knowing what type of system the OP has and how its been installed or who installed it we can only guess. I just went by typical first time set up procedures and assumed no ignition timing changes had been done.

Being the vehical is only 9 years old it likely has a knock sensor and if it went bad the computer system should give an error code for it.

Regarding retarded operation:

1. Power drops due to late combustion phasing, so the driver needs to open the throttle more...that puts more mass flow through the engine at a given torque level (as when cruising at 100 km/hr)
2. Yes with spark retard (as Andy G says) the heat flux to the head goes down - that reduces thermal load on the coolant a bit.
3. But with retard, the heat flux to the exhaust port and the surrounding water jacket goes up (due to later combustion & hotter exhaust; less energy was extracted).
4. So the the tendency of the cooling system to get hotter or cooler (with retard) depends on the balance between the heat flux to head and the heat flux to the exhaust port. Exhaust ports with more surface area (i.e. 2 exhaust valves vs. 1 exhaust valve) will pick up more heat.
5. I need to check the heat balance between the head and the exhaust port by looking at Heywood's book on engines. Somewhere in the book, he splits out typical heat balance by piston, cylinder, head, exhaust port, other...
6. Bottom line... Andy G - You may right that "over advance" will increase cooling system heat load - will occur if the heat flux to the fire deck (head /water jacket) is much bigger that the heat flux drop to the exhaust port/water jacket. Maybe you have a better answer.

If the person with the engine problem knew what the exhaust temperture was doing, relative to the petrol (gasoline) base case, that would be useful. High exhaust temperature (say 100 C hotter) would indicate retard and low exhaust temperature would indicate more advance.

I hope this is somewhat understandable.

Very understandable and I also agree with you!!

Octane has nothing to do with power or fuel consumption.

Hi Guest,

Thank you for your reply,anywhere can you explore little more of your opinion why

'Octane has nothing to do with power or fuel consumption' ?

Regards

Hi langyaw,

Thank you very much of your doc received.

Regards