Excavator is a 2001 Komatsu PC75R-2 with a brand new crate motor from Komatsu. The motor has 250 hours on it. Machine has a total of 3,000 hours on it. The radiator has been washed out and is not operating in dusty conditions. The airflow is good on the radiator, all new filters on machine, belts tight. Issue is with over-heating only sometimes, we can have the same operational conditions (digging/tramming up the side of a cliff) and the heat gauge will raise to the green/red line and we fast idle the temperature back down. Other times we run the machine just as hard under the same conditions and the max temperature we get is 160 to 165 degrees using a temperature gun. The radiator and hydraulic oil coolers sit side by side not one in front of the other on this machine. I’m thinking it may be a sticking thermostat, any suggestions?
Had some issues with a PC-40 years ago. The foam gaskets between the radiator supports and the hood disintegrated and air flow was bypassing the radiator. Fashioned some sheet metal with a rubber slip on strip to seal between the radiator and hood and problem went away.
yes, make sure any insulation/weather strip is where it is supposed to be, this will force the air to flow where it is supposed to, thru the coolers and rad, not around it.
Was it doing it with the old engine installed ? If it was the thermostat sticking i doubt you would be able to cool it by fast idling . I'd check the bottom hose is not sucking flat at full noise and returning to normal at idle . Also a thing i found once was the water pump impeller was intermitantly free wheeling , stopping the flow of water and then it would grab the shaft again and be normal . Ceramic pump impellers have a steel bush in the center which sometimes lets go . You may be able to remove a hose and hold the impeller with a (wooden) dowl or paint brush handle and see if you can get the fan to move by hand .
make sure the fan belts are tight also,
I was not the owner of the machine when the old engine was in it so I do not know whether it over heated then or not. I checked the fan belt and it is tight. I will check the bottom hose and see if it gets sucked flat. I will also check the water pump as well. I do believe I will put a new thermostat in it to see since that is the easiest and probably the cheapest and quickest route of elimination. If the therostat doesn't do it then I will focus on the the other issues. I will also check my insulation and gaskets around the radiator. Thanks for the help and your responses. I'll keep you updated.
I checked the weatherstripping around the radiator and it looked perfect and the fit was nice and snug. I checked the lower radiator hose and it was not collapsing on WOT when hot. The only reason I think it may be a thermostat issue is the temperature runs at 160 to 165 when working really hard when it should be at 180 or above and then after several hours operating like that is starts to run almost to the red line but with sitting still and not operating at a fast idle the water temperature will come down, not fast but will come down within 4 to 6 minutes to the middle operating temperature. I think the thermostat may not be closing or opening all the way. This may be the reason the engine runs cold (160 to 165) most of the time and when it gets hot under the same operating conditions it slowly cools backs down on fast idle. Any ideas or suggestions?
Cheap fix to change the thermostat. Try that and if problem persists, check to see if the gauge is functioning properly. Has it ever boiled over? Our battery always lost its water due to the high under hood temps since it was located under the hood.
what bigbob said, cheapest and easiest is thermostat if everything else checks out. let me know what you find, it may be faulty wiring,sending unit or guage. Let me know and I can get you specs for ohm reading on the temp sensor, would be nice to have you check it with a infrared temp gun and verify if it is actually getting warm or maybe a possible faulty guage,sensor or electrical problem.
Guys I really appreciate all the help and advise. I will be replacing the thermostat today and will report back the results. I will also keep my Temp gun on the hoe to verify if and when the engine gets hot. The radiator has never boiled over or the battery, it could be a bad gauge. I will report back the results, and once again, thanks for the help and I love this website.
We changed the Thermostat and that fixed the problem. We cannot get the gauge to go above half way in the green. $53 for the Thermostat and two gaskets (upper and lower), half gallon of anti-freeze and 30 minutes to correct the problem. Thanks for the help and advise
Well , i learn something new every day . Today i learnt that idleing an overheated engine can unstick a fully stuck closed thermostat .
glad to hear ya got her fixed, keep em digging....................
I dont think it was proved that the thermostat was FULLY STUCK, just that it was faulty. :drinkup
thats what i'm thinking, our WA70 did the same thing last week and that was the problem....
Seeing how a thermostat OPENS when hot and CLOSES when cold , idling a hot engine to cool it will NOT OPEN the thermostat and bring the temp back to normal . Sorry not logical .
:yup :iagree BUT if the thermostat is sticking in the part open position eg not always opening all the way then water flow is restricted and idling the engine will allow the water to flow and cool. It would be intresting to know if anybody noticed a longer time to warm the machine up to normal operating temperature, as this would suggest to me that the thermostat was not closed when cold. Probably not so noticable this time of year but when you cab heater isnt blowing warm after 5 mins on a frosty morning you know you have thermostat problems or that the last time it overheated some expert took the dam thermostat out altogether :Banghead
As it has fixed the machine it must have been the problem . The thermostat must have been faulty from new as the crate engine only had 250 hours on it . WVBartMan , did you notice what temp range the old thermostat had on it ? Depending on where the engine came from it could have had an inapropriate temp range . I know i am wrong and it has fixed the problem but something does not add up .
That is a very good point, and I hope you were not thinking I was trying to PROVE you wrong that was not my intention at all, open discussion and thoughts raises ideas and responses that another might not have thought about. As somebody commented in another thread, what is obvious to one person is not always so clear to another. :drinkup
No i was not thinking that at all , but thanks for your concern . I liken these forums to a pub , ideas get kicked around , some good some not so but in the end the correct prognosis can often be found with snippets from all (Before the affects of the beer set in).