Bosch Temperature gauge.inaccurate?

Next question: Today I installed a new 180 degree thermostat in my "94 Chevy dually with the 5.9L 12v Cummins motor because the new Bosch temperature gauge that I installed yesterday reached the 250 degree mark a few miles from home and even went beyond that to an estimated 275 degrees. But oil pressure was still good and the radiator was not blowing out coolant, nor did the motor have that "hot" smell. When I got back to my shop I used 2 of my wife's thermometers to check actual engine temperature. One is a stainless, sharp pointed meat temp. tester. The other is a glass candy thermometer. It is about a half inch wide and tapers down at the bottom to the bulb that contains the mercury. On the casting that holds the thermostat is a hole about 3/8ths of an inch wide by about an inch or so deep. It is only about an inch away from the take-off point where the line to the temperature gauge is connected to the head just behind the thermostat. I filled this hole with water while the engine was running, with the Bosch gauge showing 240 degrees. After waiting a minute for the water in that hole to reach the same temperature as the motor, I put the meat thermometer into the water. It read 165 degrees. Then I immersed the bulb at the bottom of the candy thermometer in the water in that hole and it read a steady 180 degrees, which it should inasmuch as the new thermostat opens at 180 degrees. So, would any of you care to comment on whether my method proved that the Bosch gauge is reading about 60 degrees to high? Thanks in advance.
 
Put the gauge end in some warm water and see what it reads and then put your other thermometers in it at the same time and see what the difference is. Might be more accurate than what your trying to do.
 
You can use boiling water to test. Water boils 180 degrees. Make sure the bulb is suspended in the water and not touching sides or bottom.
 
(quoted from post at 22:01:38 05/24/18) You can use boiling water to test. Water boils 180 degrees. Make sure the bulb is suspended in the water and not touching sides or bottom.

Umm, you would have to be higher than any mountain in the lower 49 states to boil water at 180 degrees.
But.......test all of the gauges in boiling water to see how they compare. My bet is on the candy one being the most accurate.

I would say the gauge or the sender (if it has one) is faulty.
 
I immersed both thermometers and the gauge sensor in a pot of hot water. All three read close to the same temperature. Actually the candy thermometer and the Bosch sensor read the same, 175 degrees. I cranked the motor while the sensor was still outside the casting where its inserted, and created a geyser of water and coolant, so that told me the new water pump was working fine. Then I reinstalled the sensor or probe, removed the radiator cap, cranked the motor and waited until the Bosch temperature gauge was reading close to 200 degrees, plenty warm enough for that 180 degree thermostat to have opened, yet I saw very little coolant trickling through the radiator vanes on the way to the bottom hose. So I removed the new thermostat altogether and replaced it with nothing. I purposefully left the radiator coolant level about 5" low. On a one hour trip the next day pulling an empty dual axle 8 x 16 utility trailer, the Bosch gauge only went up to 209 degrees. On the return trip with about a 7000# John Deere loader tractor on board, the temperature indicator still did not go above 209 degrees. This morning before leaving for about an hours worth of mostly city driving, I filled the radiator to the top with coolant. The highest reading I got on the Bosch gauge was about 159 degrees. When I returned the new thermostat to O'Reilly's, the girl said that this thermostat was not the right one for a 12v Cummins motor. But I decided to not go through the hassle of changing the thermostat again so I'm just going to drive without one until winter sets in. I would hold O'Reilly's liable for any damage to my motor but I haven't noticed any. Still runs and sounds the same.
 
Put the thermostat back in,it slows the water down and helps keep the air out of the system. Air will ruin the motor(cavitation) Every pound of PSI on the cooling system lowers the boiling point 7 deg. My Freightliner runs over 200 deg most of the time and has for 292000.0 miles so far.
 
Someone gave you bad info. Every pound of pressure RAISES the boiling point 3 deg. It also lowers the freezing point, but I don't remember how much.

Willie
 
Tough to find a good thermostat. About like condensers. We have used the actual Cummins one's and still not had good luck with them. Keep trying till you get a good one I guess.
 
Buy a cheap infrared thermometer and then you can run down the road awhile till the gauge reads hot and see what the infrared thermometer says
 
Number 1, put the right thermostat back in, 180 is too cold for that engine.

Number 2, check the gauge.
 
I had a similar problem with a 1973 Mercury Capri that I had bought
at a used car lot. Temp gauge read around 250 deg.
Installed a new thermostat that looked like the 180 deg one that
came out. Looked similar to V8 Chevrolet. Wrong!
The V6 engine was supposed to have a bypass type thermostat
made similar, but smaller, that the t-stat found in Detroit?s.
Finally got a correct one and temp ran 195 or so.
 
Right. Pressure raises boiling points. Neither do I understand how a thermostat could help keep air out of the motor. Or why that would even be a good thing if it could. As far as 180 degrees being too cool, why would that be? My old "93 Cummins Dodge dually has about a half million miles on it, and it has always maintained an engine temp. of about 160 degrees unless I am pulling something. Then it might go up to 210 or thereabouts depending on the weight and terrain. Besides, as engine temperature goes up, viscosity goes down, reducing the load carrying capacity of the crankcase oil, therefore reducing the ability of the oil to protect the engine. Is my reasoning incorrect?
 
180 is fine . Your wrong on viscosity as the temp goes up on multi viscosity oils the oil changes to the 40 weight instead of the 15 if You ever send a oil sample in they will send you a report and part of that report is what the oils viscosity is at certain temperature I don?t have any handy but I?ve never had one come back that wasn?t around 40 viscosity
 
(quoted from post at 20:05:14 05/25/18) "I immersed both thermometers and the gauge sensor in a pot of hot water. All three read close to the same temperature. Actually the candy thermometer and the Bosch sensor read the same, 175 degrees."

Comment: Is the Bosch gauge a mechanical type that uses a pressure bulb sensor or an electrical type that uses a sensor which changes resistance to sense temperature? In the case of the mechanical type the above test should yield a comparison of gauge accuracy. A better test would be to take a sample of your coolant and test at the boiling point - that is the temperature reading you are interested in. In the case of an electrical type gauge - I assume you did the test with the engine shut off. The gauge reading in this case depends on the reference voltage supplied to it. With the engine off it is battery voltage, with the engine running it could be another voltage, going down the road it could be yet another voltage.

"....Then I reinstalled the sensor or probe, removed the radiator cap, cranked the motor and waited until the Bosch temperature gauge was reading close to 200 degrees, plenty warm enough for that 180 degree thermostat to have opened, yet I saw very little coolant trickling through the radiator vanes on the way to the bottom hose."

Comment: Since the engine was idling without load it would require a very little coolant flow to maintain temperature. Your observation could indicate normal operation.

"So I removed the new thermostat altogether and replaced it with nothing."

Comment: I have more than once installed a second new thermostat until I was happy with the operation. It has been my experience drilling a bypass hole 3/32" to 1/8" in the mounting flange, many already have the hole. This allows coolant to flow past the thermostat giving it a better sampling of the actual coolant temperature. Proper engine temperature is important to maintain dry (no fuel wetting) cylinder walls. Fuel wetting washes away the oil film causing wear. Fuel economy and oil life should also improve by maintaining the proper engine temperature.
 
Thanks I.K. That was very informative. My injector pump rebuilder agrees with you. I guess I am just so skittish about overheating again that 160
sounds better than 180. But my friend who followed behind me this morning on the way to the paint shop told me later that I was smoking the entire
time, and smelling of coolant, although the coolant level in the reservoir and radiator is remaining constant, so I don't know why he would be
smelling it. So, one more trip to O'Reilly's, and a little more aggravation. But thanks again.
 
SV, I agree, yet many Dodge owners say at least 190 is better for fuel mileage, performance, and less oil consumption. I'm all for that. Apparently the whole problem with overheating I was experiencing was a stuck thermostat. I'm going to install a Stant 190 and see what happens.
 
SV, would you mind describing your truck? One of my trucks is a 1993 Dodge D-250 diesel that was converted into a D-350. It has the factory Getrag tranny and 3.54 rear end and is an extended cab. It consistently gets 20+ mpg unless I'm pulling something. But its gvw is only about 8300#, even with the full tool box and stuff in the bed. I have never changed the thermostat, and I don't exactly know how warm it's running because the dash gauge has no numbers on it, but the needle never gets to the halfway mark unless I'm pulling something heavy on a hot day. Relative to my 1994 Chevy dually with the "93 Cummins motor in it, I haven't yet determined exact fuel mileage because of a leak in the pump but I'm not expecting to get fuel mileage equal to my "93 Dodge because the Chevy is heavier and the rear end gears are 3.73. And by the way, there was no way to fit a fan shroud behind the radiator of the Chevy. The fan blades are a good 5" away from the radiator. I don't know how this will affect engine temperature.
 
It?s a 1998 3500 it?s build date is 3 of 98 but it?s a 24 valve cummins it?s has plus 50 hp injectors and an edge with attitude 5 stage programmer the flat bed is home made is 8 feet long and and 8 feet wide it has a tool box and a diesel compressor on it . My 94 3500 weighed 8500 with the same tool box and air compressor it would pull 650 miles gallons out of 33 gallon of fuel everytime . I just got home from hauling a 17,000 pound load 230 miles and averaged 13.55 mpg I was running 80 mph the whole way
 
If you guys had pyrometers, on those engines, and looked at them you would not pull them till they got to the 200 range. The pyro would be so hot. On my cats if you pull that hot the exhaust temp(pyrometer) is way to high for my liking. I quit with about 1000-1100 this is about 190 no more than 200 water temp.
As for the temp problem put the thermostat in water and heat till it opens with the candy thermometer in the water to see what it opens at. I have gotten bad ones new.
 
I?ve had a pyro on every diesel truck I?ve ever owned and even the other day when I boiled over pulling a big hill because I forgot to rake the cardboard out the egt still wasn?t over 1250
 
The scuttlebutt on the truck forums is that Stant makes the best thermostats but I couldn't find a 190 degree one for a "93 12v Cummins, but Stant does make a 195 degree one so I ordered it. It came in the other day, along with the new heavy o-ring I ordered. I installed it, cranked er up and went tooling down the road. Engine temperature hovered between 195 and 205. I'm okay with that. At this point I'm wondering if we might have installed that new 180 degree Bosch thermostat backwards. Oh well, no harm done apparently, and now my engine temperature should be at max for fuel economy, power, lubrication and minimal oil consumption. And I think maybe that my habit of dumping about 3-5 gallons of filtered used motor oil into the fuel tank at every fillup probably helped to prevent damage to the motor when it ran so hot.
 

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