Trouble Shooting "Low" Operating Temperature

[SPYDERLK]

I don't know the technical reason that manufacturers increased cooling system pressures over the years. But 4 PSI systems were common in years past. See RADIATOR 4 pound Pressure Cap - Wayne WR-5 New Old Stock #2. And we all know that much of the engineering in these Chinese tractors dates back many years as well.

So on this Jinma, we're talking quite low coolant system pressure - about 4.3 PSI. The pressure that pushes against the relief spring in the cap is the same as that which pushes against all the seams, hoses, fasteners, seals, and gaskets. I've seen a 15 PSI pressure cap on a 200 Series Jinma cause hot coolant weep profusely; underneath hose clamps, through radiator tank crimps, past sending unit threads. Stop them, and it starts pushing on the pump seal.

[[[As I'm sure you're well aware, cooling system leaks influence operating temperature - and that operating temperature is reflected by the temperature gauge.]]] Hence, a 15 PSI cap on a 200 Series Jinma can skew temp gauge readings. But I only asked the OP the cap question, as one step in the troubleshooting process. Since he's still using the OE cap, this doesn't apply.

SMALLJOBS - Having said all that, the OE cap springs aren't very robust. As part of your repair effort, I personally recommend a low pressure aftermarket cap. Don't hold me to this number - I don't have those Jinmas anymore. But I'm thinkin' I used a Stant 10282 on them. If you hunt long enough, you may .eventually find an old 4 PSI cap to fit. Short of that I found the 7 PSI Stant to stop the weeping caused by it's stouter 15 PSI cousin.

//greg//

[[[Yes, now I see. If it leaks long enuf to lower the coolant level it makes it run hotter. To me this is causing the gauge to read differently, altho probably not skewing it. However, once enuf coolant is lost, causing many alarming indications, the gauge wont be immersed in coolant and may start to read low. That would be skew.]]]
The OPs tractor is full of coolant and is running cool. The pressure cap is not the issue even if it were a high one. Your point that he should not use a high pressure cap is distinct from this, and a valuable point of information.

Oh, and the reason for increasing coolant pressure is to allow the coolant to run hotter w/o boiling. [This is a particular problem in todays higher performance power systems where boiling can be a problem hidden in hot spots of the engine.] To a certain extent anti freeze elevates the boiling temp, but the heat exchange efficiency of the coolant decreases slightly as the water concentration goes down. Essentially you want enuf anti freeze for freeze prevention - and then take care of whatever extra boil resistance you need by increasing the pressure.
larry

 

[Bob Rooks]

Anti-freeze per se is falling by the wayside throughout the industry as coolants with SCA's are becoming more prevalent, convenient, and desirable, such as the Final Charge brand.
Engines must run warmer to meet emission standards, so thus have higher thermal effencies - the hotter, the better (to a point).

 

[SPYDERLK]

SCAs?.....

 

[greg_g]

SCAs?.....

Supplemental Coolant Additive; a chemical package that is added to coolant either as a liquid, powder, or charge inside a filter. Most commonly formulated to combat cavitation and corrosion. You can buy it as a concentrated additive from auto parts stores, or in pre-mixed containers, most commonly gallons. Most anti-freeze companies make at least one; this Florida list alone ( http://www.doacs.state.fl.us/standard/petro/afbrands.html ) lists about a dozen and a half. The stuff's good for all liquid cooled engines, although it's most commonly sold to diesel operators - and is considered a must for wet-sleeved diesels. Owing primarily to availability, I use Peak Final Charge 50/50 premix - although I have also used the NAPA concentrate (NAPACool, I think).

//greg//

 

[Smalljobs]

Replaced sensor, checked sensor case to ground OK, started up tractor, no improvement. I opened radiator cap and put cardboard in front of radiator until temp reached 80C as measured inside top of radiator. Gage still won't go much over 40C.

I give up and will add a regular mechanical temp gage. If the gage and wiring is too sensitive to resistance I don't want to spend any more time on it.

 

[greg_g]

If the gage and wiring is too sensitive to resistance I don't want to spend any more time on it.

I sympathize. But it's not that the gauge and wiring are too sensitive, they're just cheap. That said, I've had no problems with temp indications on my 4 Chinese tractors. Luck of the draw maybe. But given the circumstances, you have the right idea going aftermarket.

//greg//

 

[Smalljobs]

Does anyone know the thread spec on the male end of the sensor? I went to the autoparts store and found a mechanical gage including "metric" adapters. Even I bring the sensor along, it's a male thread so there is no way to really check the adapters that come with the gage.

 

[Bob Rooks]

I give up and will add a regular mechanical temp gage. If the gage and wiring is too sensitive to resistance I don't want to spend any more time on it.

Unless you are very cost concious, I recommend the Murphy Switchgageï®.
I have one for jacket water temp. and one for oil pressure. They have adjustable setpoints for alarms and indicators.

 

[Smalljobs]

Verified thread in engine is 3/8 NPT and the Autozone gauge and threaded adapters will fit fine. Will install and close this out. Thanks for everybody's help.