I have a 742 (Ford FL98 Gas Engine) that has had an overheating issue since I got it a few years ago. It almost seems like the cooling system just can't keep up when the ambient temperature is above 85 or 90 degrees. If it is idleing it is fine, but once I start driving, and/or using the hyraulics the temp steadily rises. Over the last few years I have replaced the water pump, thermostat, radiator, and muffler. The engine was also rebuilt when I got it and I replaced the head on it because the previous head had a crack that had been repaired. The fan is working, the shroud is intact, and the oil cooler is clear. I have also added two elecrtic "sucker" fans on the top side of the radiator. I have tried running it at different RPM's and played with the choke to try different air/fuel mixtures. The timing is also set to the specifications in the manual. It seems to do fine when it is cool outside, but if it is above 90 or 100 degrees, it overheates within about 5 to 10 minutes. Is it just that the gas Bobcats aren't designed for warm climates?
Overheating 742
- Thread starter ma107
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OldMachinist
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If you're using the gauge reading to determine that its overheating have you verified that its correct. Could be a bad gauge or sending unit giving false readings.
Cyclone Ranger
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Here are a few things I would try:
Confirm that the vacuum advance diaphragm will hold a vacuum by sucking on the inlet. It should not leak. Also confirm that the mechanical advance is functioning by disconnecting the vacuum advance and confirming with a timing light (preferable a dial-back style) that the spark is advancing as rpms increase. The manual has a table showing advance as a function of RPMs. Confirm that your valve lash is set properly. Confirm that you are using a 50/50 coolant mix and that the radiator is full to the top when the cap is removed (when cool of course). Confirm that both the oil cooler and the radiator are clear by blowing high pressure air from the bottom upward through the radiator. As stated earlier, verify the temp sender and gauge is accurate.
Good luck.
Thanks for the input, I really appreciate it. The temp gauge is an aftermarket one that I have added, and I have verified it with a non contact thermometer, so it appears accurate. I have replace the radiator cap and done pressure tests on the cooling system and I have found no leaks. It is topped of with a 50/50 coolant water mix in it right now, and I have also experimented some over the past years with additives that claim to help lower temperatures, but I haven't noticed any remarkable difference. I have checked the timing advance in the past, but I will spend a little time checking that next time I work on it, and I will also check the valve lash. Thanks again for the input, I will post if I ever figure it out.
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the thermostat can only be as accurate as the sender unit
I realize this is old but I'm curious to know if it's been resolved and/or if anyone has anything to add. Mine runs very hot all the time and I'm looking for help also. It doesn't feel like it moves enough air. I know someone with a 763 and it blows so much air at idle but mine (742) blows almost none. Also, mine sucks in around the cab and up though the oil cooler and rad whereas his draws down through the rad and out around the cab... The exact opposite of mine. Pat
A 763 will blow more air than the odler machines, the blower is really good.
Are the covers in place above the engine? There should be plates that cover an opening in the blower housing that allows access to the oil cooler. Is the oil cooler and radiator fins clear?
