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  • CNG operating temps

    Does CNG run the engine hotter than gasoline?
    I'm especially concerned about what motor oil to put in my car...should a put in a heavier one coz my car runs more on CNG?
    And whats with the especially-for-CNG motor oils in the market?

  • #2
    Re: CNG operating temps

    There is nothing that will inherently make a CNG engine run any hotter than a gasoline engine. This is more determined by engine design than the fuel type. On average, I'd say most CNG engines would run with a slightly lower head temp, simply because the amount of energy produced per unit area would be lower. As for CNG specific motor oil, I've never actually seen anything like that, but my guess is it'd be much like any other 'specialized' motor oil, in that it is a more expensive version of pretty much the same stuff.
    1997 Factory Crown Victoria w/ extended tanks ~~ Clunkerized!
    2000 Bi-Fuel Expedition --> ~~ Sold ~~ <--

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    • #3
      Re: CNG operating temps

      About the temperature thing, I used to have a 1984 Daihatsu Charade that had run all its life on gasoline, which I got converted to CNG. After that it started heating up, and I had to change the radiator and fan to get things back to normal. Now given that the conversion did not effect the radiator or the water body in the engine, and the car was running perfectly normal before on its existing cooling system, if the engine was actually running at the same temperature why would the car start heating up?

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      • #4
        Re: CNG operating temps

        Run whatever oil is recommended for the gasoline engine if you are bifuel, you won't have any problems. Just change the oil at regular intervals. Although you have reduced the amounts of hard carbon from incomplete combustion and the posibliity of oil dilution from unburt fuel, you have to be concerned with thermal breakdown and general contaminants from normal operation. You can extend oil change intervals running straight cng, but I would choose not to unless I did some oil analysis to see how th oil was holding up.

        Combustion chamber tempers are slightly higher (not enough to worry about) because there is no cooling of the cylinder by the vaporization of a liquid fuel (gasoline) in the cylinder.

        Hope this helps

        Larrycng

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        • #5
          Re: CNG operating temps

          As for the matter of temperature, CNG burns at 1,000-1,100°F, gasoline burns at half that. Hence the need for hardened exhaust valves and seats. Most heads are cast iron and don't dissipate heat as well as aluminum would. Most engine cooling systems are designed with restrictions, i.e. the thermostat, that control the amount of coolant flow as to ensure enough time in the radiator to actually dissipate the heat. Any change to that engine would dictate a re-evaluation of the cooling system including a larger or additional radiators.

          Sorry to duplicate Larry, you typed faster than I did.

          As for the lack of liquid fuel vaporization, I'm sure the JT effect of gas expansion near the intake valve, i.e. replacement of stock gas injectors with CNG injectors, would actually meet or exceed the cooling effects of vaporization.
          Unless of course your fumigating far upstream, then you'd have little to no advantage. I've seen some installs were the charge actually had more time to heat up instead of cool down.
          Last edited by cnghal; 06-06-2009, 09:37 AM.
          Your Friendly Nazi Squirrel Administrator

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          • #6
            Re: CNG operating temps

            I was under the impression the hardened seats were due to the lack of lubricants that are present/added to gasoline.
            1997 Factory Crown Victoria w/ extended tanks ~~ Clunkerized!
            2000 Bi-Fuel Expedition --> ~~ Sold ~~ <--

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            • #7
              Re: CNG operating temps

              Hey so are we agreed that an engine would run hotter on CNG? I mean significantly hotter...as suggested by all the difference in combustion temps b/w cng and gasoline. What's the consensus guys?

              And how does the gas expansion/gasoline vaporization relate to a carburetored engine?

              Second, any visual tips for checking how the oil is holding up so far? I put in Zic synthetic...

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              • #8
                Re: CNG operating temps

                Philcal,
                Running too lean on gas or CNG, carb or injection, can burn up an engine in short order. If you seem to run hotter on CNG only, I'd check your mixture, especially if you're using a carb/mixer with no O2 sensor feedback.
                I'm getting the feeling you haven't given us the full story. What vehicle type, engine, fuel(s), carb or injected are you running?
                Last edited by cnghal; 06-06-2009, 04:39 PM.
                Your Friendly Nazi Squirrel Administrator

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                • #9
                  Re: CNG operating temps

                  Hi guys, back from goofing off.

                  I just got up earlier than you did Hal. I haven't tried checking temperature drops, but I would probably disagree with you on the injected gasoline and CNG having similar cooling effect especially when the highest rail pressures I've seen around 110 to 120 psi. If you were injecting CNG at much higher pressure, say what would be necessary for direct injection, I might tend to agree --makes for some good discussion and research.

                  If you run CNG rich, above about 1% CO was the figure I was give from one of the "old guys" in the business, you tend to run hotter and will tend to melt pistons for the same reason; lack of cooling from vaporization of the liquid fuel. When you're are climbing out in piston engine aircraft to go a little rich, no only for power, but for cylinder head cooling. When you get to cruise altitude you lean to peak EGT and then go about 50 degrees rich to keep CHT a little lower -- you suggested that, lean does run hotter

                  I agree we need to know the specific vehicle, engine, fuel system and application. If he is talking about the '84 Diahatsu mentioned earlier, I would guess carburetion, was running rich on a fumigation system and probably had a mimimal or defective cooling system. The Diahatsu didn't last long in this country.

                  Take care

                  Larrycng

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                  • #10
                    Re: CNG operating temps

                    Hello everyone, If you are running a dedicated natural gas vehicle then I would seek out a specific motor oil for natural gas vehicles that has a low ash content. I believe that Mobil corp produced it, but I would not recommend using it if the correct weight and engine spec is unavailable. I strongly agree with Larry that testing (of the oil) should definately be used to determine a proper interval. I have been told that one transit bus had 55K miles on the same oil, and the additive package was still intact! I do like the system from Mercedes that measures particulate by sending out a laser beam through the oil to determine the level of suspendid debris, but that doesn't necessarily determine if the additive package is still intact. As far as your engine heat issue, I would strongly suspect some type of mechanical failure, based on what you are describing. I strongly doubt that it is related to the NG system. I would definately switch to Inconel valve seats, but I would only do so if, or when I experience valve recession issues or a head gasket failure. Stainless valves on the intake and inconel on the exhaust is also money well spent. As far as a NG cooling system running hotter. I doubt it. The process that is occuring at the high pressure regulator is actually reducing the load on the cooling system. Yes the valves and seats WILL run hotter but that should not be reflected in higher cooling system operating temps. With dry fuels on dedicated NG vehicles, be sure to provide a fresh air inlet to the exterior of the engine bay. Any drop in inlet temperature will correspond to a drop in exhaust gas temperature. Also it is permissible on dedicated conversions to CNG or LPG to disable the heat riser pasages in the intake manifold, as well as eliminate any heat stove pipe as they are irrelevant on a dry fuel system and will hurt the production of horsepower.

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                    • #11
                      Re: CNG operating temps

                      Have any of you used a heat sensor (laser, or something, the one that looks like a gun, and practically you aim it at the objetive?)

                      I've found most of the cases, the temp is lower on CNG. The flame temperature has no direct relation to the engine temperature, but it does the burning speed. This has to be corrected by the timming. If we have an engine with 200 hp (gasoline) and on CNG it is 120 HP, that means you are transfering most of the chemical energy into thermal energy. if you start messing with the timming to achieve more power, be sure that as much as you approach to the original power (if you are not turbocharged, and boost up on CNG, will never be the same) is the lower you are damaging the engine. With CNG, More power = more lifetime.


                      Anyway, regarding to seats and lubricants, and... nothing. The valve that suffers the most is the exhaust. This is due to the temperature on it. The intake valve, has no difference on the temperature than can be decreased by gasoline vaporization, as it is low temperature. Anyway, the cold air is more than enough to cool it down.
                      The exhaust, in the other hand, only cools when is full contact with the seat. This is why some people use to give more gap to it, which (even short) gives few more time to cool it.

                      But, as I said before, the main issue is Timming. Remember that the engine is a thermo-dynamic machine. Whatever you don't convert into mechanical energy... you know where it goes.

                      Sorry if this bother someone... please let me know.

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                      • #12
                        Re: CNG operating temps

                        I would love to bump the timing on my car to see if I could get more power but Toyota ECU's are a bugger to mess with and piggyback computers, well they have their whole mess as well. I have tuning equipment to tune GM's and Ford's but I settled on a Toyota.
                        Michael Williams
                        2001 Toyota Camry

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                        • #13
                          Re: CNG operating temps

                          If you have the old system (integrated coil+distributor) if I'm not wrong, you could use a 515 Timming Advance Processor from AEB.
                          If you have CKP wheel (36, 60 teeth, any kind) you can use a ARF from Tomasetto Achille which is programmable (every 400 RPM you can set how many degrees, and trigger it by TPS if needed). If you cannot get it, also a 510T (AEB) I'm quite sure it works.

                          Or, if you dare, to open the distributor and cut the internal wire from the module to the coil, there you can set a Wolf from AEB or a APW from Tomasetto Achille. I've made this, I wouldn't recommend it if you're not expertise on wiring, but if you are, is easy

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