85 300TDT engine temp is high with all new parts
 

Here is a stumper: 1985 300tdt w/275K. Engine has not beeen rebuilt but is tight with good compression. New water pump, radiator, thermostat & coolant. Engine runs hot at 100C during normal driving. Ran same temp before upgrades but wanted to to them anyway. Never overheats or gets hotter than 105 yet top of radiator is hot yet bottom hose is cool. Runs cool at 50-70 when thermostat is removed. New themostat from dealer. Old one has same effect. Two defective thermostats? Oh yeah, heater inlet to interior will bake a potato if you crank it on high with either thermostat in.

did you make sure all air is out of the system? an air bubble could be stuck somewhere in the head causing a hot spot..

Well, the SD is in a similar situation.

Starts to run a bit warm.......up near 95°C. or so.......especially in conditions of low airflow. After a highway run and then down to the stoplight runs, the temp will climb to just about 100°C. and sit there. It won't come back until the vehicle gets back on the highway and then it will slowly (30 minutes or more) return to 90°C.

The interesting thing about it is that a brand new OE thermostat performs in the identical manner to the 22 year old unit that was removed. Absolutely no change in performance. The radiator is probably original and the water pump is one year old.

An infrared temperature sensor verified that the outlet temperature to the radiator, measured right at the thermostat housing was 85°C. and the gauge was at 95°C. Checking the temperature of the head also confirmed that it's running at about 85°C. as well. So, the guage is definitely reading 10°C. higher than normal.

However, this vehicle never moved above 90°C. on the gauge unless the ambient temps were well into the '90s. It's sitting at 100°C. on occasion with the ambient temp in the '60s. Quite strange.

I have not pulled and cleaned the radiator and I suspect that it's part of the problem. But, considering that you have a brand new radiator and it's doing the same thing, this might not be the culprit.

I would urge you to check the outlet temperature with an infrared measuring gun and see if the gauge is way off the mark.

what temp is marked on the stats?

tom w

80° on both new and old.

All air is out of system. Both thermos are 80 degree. The puzzler is why the lower radiator hose is cool to the touch. Could 2 thermos be bad?
As I stated earlier, temp is cool when thermostats removed.

Having both stats be NG is highly unlikely.

As mentioned, the gauge may be reading high. Can you borrow an infrared temperature gun to measure the outlet temp at the thermostat housing?

Perhaps the gauge could be reading high yet should not the bottom radiator hose be almost as warm to the touch as the upper after a warm-up run? Why is the interior of the car so hot with the heater on? I have had several other 123's yet this is a unique problem.

The return coolant is much cooler than the coolant from the head. I measured 54°C. as a return temperature at the outside of the hose. The coolant would be somewhat higher.

my car is the same way. on a hot summer day, 90 to 100 degF ambient the water temp guage is nailed to 95, no matter what driving conditions. but whenever it is raining or night time driving it goes up to 100, then goes back to 95, it fluctuates back and forth, up and down, and so on, especially now that the ambient temps here is now ranging from higher 80's and lower 70's, high and low. it always acts this way since i got the car, different beahvior each season, never had any problem, so i think it is normal for this particular car. but i want a new plastic 9 blade fan, because i think my current 9 blade aluminum is now too heavy for my old fan clutch.
anyway, my analysis tells me that the reason it is behaving weird like this is, i think that the fluid in the radiator is too cold when ambient temp is not that hot, therefore when the thermostat opens the cold water from the radiator immediately shuts the thermostat down until it becomes hot again to trigger it to open and allow the cold fluid to cool the engine again and shut the thermostat, and so on, hence the gauge fluctuation. hot. cold. hot. cold. hot. cold....

This conclusion is not based upon fact. If this was the true situation, then everyone with a 617 would experience the same behavior. The fact that they don't rules it out.

I think somebody on the board had 4 faulty thermostats! :eek:

I run mine all day at just 2mm above the 80 mark (~85 deg C). With AC on, it would go to 90 but stay there.

Most likely not bad stats. What about trying a lower temp stat. They do come in 2 or 3 different temp ratings.

If you removed the thermostat for troubleshooting purposes would you be able to rule it out as a culprit ? You coud take the thermosat and put it in a pan of water then heat it up and then verify when it physically opens with a thermometer . I also have seen high temps at highspeeds caused by a bad lower radiator hose,the springs were damaged and allowed the lower hose to collapse and waterflow was restricted to the water pump (lots of money and parts were replaced instead of a 5 dollar hose).good luck,Johnny:confused:

Good point on the bad hoses... it does happen.... just replace them...