Erratic temp indicator
 

1985 300D...
Lately, the temperature guage has been fluctuating between 90 and 100. For example, it'll indicate 100 and then drop in a few seconds to 90 then go back up to 100. Very disconcerting.

Also, I know there is a water leak in the front of the engine somewhere around the fan shaft. Sometimes it drips quite fast and then not at all. Anybody, familiar with this problem?

Thanks for any help!
dave

On your erratic temp. reading check that you have good grounds.
On your leakage problem sounds like your water pump is leaking and needs replaceing.

thank you, yuke!

i am in mexico and there a lot of shade tree mecanicos here. is the water pump replacement something they could handle or is it very complicated (requiring special tools, etc.)?

thank you for your time...

The temp fluctuation and the water pump leaking may be related. If it leaks enough to get sufficient air in the system, the sensor is likely to see a fluctuation.

The difficult part of the water pump replacement is the possibility of corrosion making the bolts hard to remove. If they rush this, and resort to brute force,there is a huge risk of snapping off the bolts and then could get worse from there if your not careful. This would mean drilling out the broken bolts.

The best course of action might be to soak those bolts with limescale remover. The next best thing would be rust penetrant. Then work them back and forth by slightly tightening and then loosening until you get freedom of motion. It might take repeat cycles of this over time to get them to break free. Don't rush it! (While you are waiting for the parts to arrive.)

Nothing special, shade tree mechanic should be able to handle it, with the caution about rusted / broken bolts being observed. Been there, done that, broke a bolt. In my case, I simply drilled that hole out for the next larger size bolt, cut new threads, and called it good.

Please get a genuine Mercedes rebuilt water pump; it will have a cast impeller of the correct dimensions. Aftermarket pumps are notorious for stamped impellers that don't move enough water and then you've got overheating problems.

thank you, Max! this type of advice is invaluable. not something I can just find at my local Mexican mechanic :)

thank you Blue! You are very kind to take the time to help me out. I appreciate it! :)

I agree with SD Blue you need to put on a new Water Pump before it can be tested.

I just did that on mine last month. Mine came off OK but the Prior Owner had previously changed the Water Pump (which was made in Japan) and one of the Bolts was busted off.

Bolts breaking off removing the Water Pump the Housing behind the Water Pump and the Thermostat Housing are very common. I was lucky I escaped that problem.

I did not bother to remove the busted Bolt as it has never leaked around the Gasket.

Note that a failing Thermostat can also cause temp fluctuation but you will not know till the water pump is replaced.