Jinma 284 overheating - thermostat part number?

[nepa]

Gee! I didn't mean to start an arguement here. I pulled the original thermostat this morning. It is marked 72 degrees. The arch that holds the small shaft (not the large arch that houses the spring and copper pellet) was broken and a bit deformed. I am not going to bother to test it because it needs to be replaced anyway. The housing was sealed with both a gasket and blue stuff - RTV? Will RTV without a gasket provide a good enough seal? There is less then quarter inch of mating surface between the upper and lower housing. Thanks.

 

[RonMar]

Since the upper thermostat housing comes off in your hand, it is a simple process to tap out a new gasket for it. Get a sheet of gasket material when you get the thermostat. Hold the material against the housing surface(with all the other blue stuff removed of course) and use a small hammer to tap thru the gasket material against all the edges of the housing. This tapping against the edges will cause the edges to cut thru the material and quickly form the gasket shape. I have a very small ball-peen hammer I use for this, and the round end of the hammer head works great for this, especially where the bolt holes are located.

I do not like to use just silicon as a sealant unless the housing has a machined groove where it is applied to allow it to form something like an "o-ring" crossection. Two flat surfaces usually means a gasket or a specifically engineered sealant like Hondabond used to join engine cases in honda engines.

As to thermostat removal for troubleshooting, I am sure there may be cases where removing a thermost may cause a system to fail to cool. In my experience I have yet to see a system with the thermostat removed run anything but cooler, unless there was some OTHER problem with the system(bad pump, clogged coolant passages)... I do not do this professionally, but I have troubleshot and worked on a LOT of systems over the years and it has always been a valid troubleshooting step, as well as putting the thermostat in your hand which in this case revealed some obvious issues...

.02 delivered...

 

[Rich Waugh]

I have no argument with anyone who wants to remove their thermostat; I just don't do it on my engines.

Removing a thermostat for troubleshooting is a perfectly valid technique and I've used it in the field where there wasn't a good way to test the 'stat otherwise. I just won't run an engine for any length of time under load with the 'stat out as I have seen engines overheated this way. I live din Phoenix for about ten years and folks new to the valley would sometimes think they could improve their engine's cooling by removing the 'stat. Some of them succeeded in overheating their engines and ruining them, others got away with it. I never bothered really studying why one cooked and the next one didn't, since I just tend to think that engineered systems are best run as designed.

 

[greg_g]

I too consider that gasket-inna-tube stuff insufficient, more often than not - counterproductive. That particular gasket is dead simple to hand cut. I bought two rolls of bulk gasket material from NAPA I'll bet 10 years ago: one cork, one oil/gas. As long as the gasket I need to cut is smaller than the bulk roll, I refuse to waste money on those cheap paper Chinese OE gaskets

And a 72C thermostat is not unusual. I think the Chinese assemblers just install whatever is on sale that week. In your engine I've also seen 70, and 80, and 85 degree thermostats. Buy what you're comfortable with, just don't cheap out and stick in one of those 195F on-road thermostats

//greg//

 

[quicksandfarmer]

I agree with Bob. Depending upon ambient conditions, running this particular engine w/o the thermostat can actually make it run too cold.

This I agree with. I am in no way advocating removing the thermostat as anything other than a diagnostic step. The original poster had said, "he could not go 200 yards before the temp gauge started climbing quickly toward 100," which is consistent with a stuck thermostat (and what the problem turned out to be). The thermostat is there for a purpose, its purpose is to keep the engine from running too cold.

That said, the notion that removing the thermostat can make the engine run too hot is just wrong. The thermostat is a valve, it opens more the hotter the temperature. Removing it is functionally equivalent to having it open all the way, which is the state it should be in when the coolant temperature is at or above the thermostat rating temperature.

Bob wrote:

"The engine is cooled by relatively cool coolant returning from the radiator. The heat capacity is directly related to the product of the flow times the temperature difference between the cylinder head (where the heat is mainly generated) and the returning coolant. When the system is working right the thermostat starts to open when the head gets to the thermostat temperature, say 190F. A stream of hot coolant at almost 200F reaches the radiator and the radiator loses the heat proportionally to the difference between the air temperature and the coolant temperature. That is the critical part: if the air is 100F and the coolant is 200F, twice as much heat is cast off as it would be if the coolant is 150F. Without a thermostat to keep the radiator inlet temperature as high as practical, the radiator can't get rid of heat as fast as it should. When the system becomes saturated with overheated coolant, which is common if the thermostat is removed, the engine is overheated."

This is just proof that you can't believe everything you read on the Internet. "Without a thermostat to keep the radiator inlet temperature as high as practical, the radiator can't get rid of heat as fast as it should." In what way does the thermostat function to keep the radiator inlet temperature high? That's not its job at all. Its job is to limit the amount of coolant flowing into the radiator to keep the engine temperature constant. With the thermostat removed all of the coolant flows through the radiator, and the engine runs cooler than it would if the thermostat were limiting the flow. It's true that without the thermostat the radiator inlet temperature is lower, because the radiator inlet temperature is the cylinder head temperature, and the engine runs cooler without the thermostat.

The quote does get one thing right "The heat capacity is directly related to the product of the flow times the temperature difference between the cylinder head (where the heat is mainly generated) and the returning coolant." Although I would put it differently, the heat dispersion of the radiator is the flow times the temperature difference between the entering coolant and the returning coolant. I'd say that because the radiator is where the heat is lost. With the thermostat out, the flow in the radiator is always going to be greater than with the thermostat in, and the heat dispersed is always greater too. If the heat dispersed were not greater the engine would run hotter, which would mean the temperature differential would be greater, which would mean that both contributors to heat dispersal -- flow and temperature differential -- are greater, which is not possible if heat dispersal is less.

 

[quicksandfarmer]

I have no argument with anyone who wants to remove their thermostat; I just don't do it on my engines.

Removing a thermostat for troubleshooting is a perfectly valid technique and I've used it in the field where there wasn't a good way to test the 'stat otherwise. I just won't run an engine for any length of time under load with the 'stat out as I have seen engines overheated this way. I live din Phoenix for about ten years and folks new to the valley would sometimes think they could improve their engine's cooling by removing the 'stat. Some of them succeeded in overheating their engines and ruining them, others got away with it. I never bothered really studying why one cooked and the next one didn't, since I just tend to think that engineered systems are best run as designed.

I actually agree that removing the thermostat isn't a fix for anything, it's there for a reason. And I'll offer a hypothesis for why some engines without thermostats cooked: they had a problem and it wasn't the thermostat. If your radiator is clogged or you're losing coolant or your head gasket is leaking, removing the thermostat isn't going to help one bit. A problem may begin with a stuck thermostat, but the nature of cooling systems is that problems beget more problems, as overheating leads to coolant losses and head gasket damage.

 

[nepa]

A lot of smart people here. I put in a NAPA THM169 and all is fine. RonMar's advice on gasket making and RTV is right on and I was given the same at the NAPA store even before I read the post. As RonMar said, the RTV needs a groove in one of the mating surfaces in order to work. The THM169 is 180 degrees and NAPA said that they did not have a cooler one. My tractor is now running at about 90 degrees plus or minus about 5. With the original 72 degree thermostat the engine ran at about 72 but would go to 95 under continuous heavy load. Thermostats are inexpensive. The arch that broke on the original was much more substantial on the NAPA. If I am going through the trouble of taking the housing apart I would automatically just replace the thermostat. As opposed to one post, I would never run with plain water because I often run my tractor under continuous heavy load and need the higher boiling point of antifreeze. For the same reason, I use synthetic Rotella as I feel that it can handle high engine temps at full rpm better. Again, thanks all for the advice.

 

[Rich Waugh]

You can never go wrong by using the best lubricants and coolants available. I have always maintained that frequent oil changes using high-grade oil will double the life of virtually any engine. The more stressed the engine is, the more important it is to maintain the lubrication properly. The best example of this is little air-cooled engines on lawnmowers and the like - I've gotten over two thousand hours of use from a 10 hp low-budget Tecumseh engine on a generator that carried me through the aftermath of several hurricanes without a hiccup. I changed the break-in oil at one hour and again at five hours and every fifty hours thereafter and that engine was still starting on the first pull and running strong when the alternator disintegrated after more than two thousand hours of hard use. I treat my tractor and other rolling stock the same way and it has certainly paid off over the years.

 

[Bob Rooks]

The thermostat is there for a purpose, its purpose is to keep the engine from running too cold.
OK?

This is just proof that you can't believe everything you read on the Internet.

Try this then. I consider it a very reputable source. After you finish reading this you may have a better understanding of cooling systems. This goes in greater depth in Cat school. http://www.cat.com/cda/files/3375380/

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[Rich Waugh]

That Cat publication is a really good read Bob, thanks! I've saved that in my folder of various manuals since I know I'll be referring to it in the future. It does a very good job of explaining the workings of cooling systems, a bunch of which I had no idea even existed - but then, I don't play in the big leagues with 1000+ HP engines like you do. Even so, I like learning about the way they work. I'll be studying that manual for a few nights, I'm sure.