95 E300D, when should the original coolant related hoses be replaced?
 

We're planning a fairly long trip from north Texas & plan to take the E300D for the quietness and comfort.

As far as I know all the hoses are original. They still feel and look like almost new hoses. No sign of potential failure.

I've been creating a list of the installed hoses ( about ten, plus expansion tank ). Luckily all but two have visible part numbers ( the small long hose from driver side upper radiator to the expansion tank,

and the one that connects what is probably driver side heater outlets to a hose that goes through a grommet & connects to the wiper spray reservoir plus a metal pipe near the oil filter ) I think that part # is 124 830 55 15 but not sure since it is not showing on the hose.

So my questions are:

Should I replace the hoses or can they be expected to last for a few more years?

What is the purpose of the small diameter hose that connects to the top of the radiator above the large driver side upper hose? It goes about five feet and connects to a small plastic fitting on the upper left side of the expansion tank.

I'll try to attach pictures of both of those hoses.

Those original hoses are remarkably sturdy. My guess would be that they have significant life left. I'm all original on my 91 and have no concerns.

I agree. I think hoses on my 95 E300 are original at 290k. Small hose lets radiator "vent".

as long as you have good servicable coolant in the engine and no oil on the hoses, they would be perfect.

oil soaked hoses are what give up

On the first photo ours had a previously epoxied crack in the Y that turns down. Weeping coolant, hard to spot till I got a headlamp on it while the engine was running.
I'd take a close look at that as the hoses are molded to the plastic which crumbled when I took it out.

I will go the guys above a step more - my 300SD still has the original hoses and it is a 1981 - I know because I am the original owner. So I think yours are probably going to last a bit longer.

Coolent hoses
 

my 1991 300D has still the original hoses and they still look and feel alright.
Also still have original master brake cylinder but I intend to change it this year, mileage of car 140.000

Coolant hoses will be good right up to the time they are not.

Hoses fail from the inside where you can't see. The inner liner deteriorates, cracks and allows coolant to migrate into the fabric reinforcement causing it ( and the bond between fabric and inner liner ) to degrade. The outer liner is just there to protect the fabric. Really old coolant hoses were a single layer with exposed fabric.

Internal hose failures tend to occur at the transition between hose and start of the barb. This is due to flexing and a build up of corrosion. External hose failures can occur at any rub point / oil leak

When I got my 97 SL320 124 K miles in 2011, I replaced all coolant hoses , bypassed the heated windshield and washer bottle. All hoses on my 97 C280 162 K miles purchased in 2014 were replaced as well.

All hoses were purchased from the evil dealer network, at pricing I'd expect to pay at any auto parts for a more common car. One hose for the SL come from Germany with a 2 - 3 day turnaround. Parts stocked in the US were a 1 - 2 day turnaround. It pays to have a good relationship with the parts dept and not storm out ranting about a $ 5 part that can be had for $ 4.99 down the street.

E300
 

I have the exact same car and recently did a 300k mile coolant system preventative maintenance overhaul. I replaced all of the hoses that they still sell and in looking at my 95 hoses amazingly they looked great. There are several little ones up by the coolant change over valve near the battery that are no longer available. My plan for these was to carry some short sections of heater hose so that if one let go i could bypass the culprit. There is also a couple of really tough to get to hoses over by the brake booster that have plastic fittings which make me nervous also.

I also replaced my radiator, clamps, waterpump, overflow hose & elbow, thermostat and o-rings all which were orginal.

Oh, and it looks like you have the wrong coolant in your car judging by the pic of the overflow tank. May want to do a flush of that anyway.

I've used the G-05 coolant since purchasing the 95 E300D several years ago. I do add a small bottle of ultraviolet light traceable dye to help find coolant leaks. I check for those about every three months.

This pdf says that G-05 is still ok to use. What is the benefit of changing & what is the latest best?

https://www.mbca.org/sites/default/files/antifreedec04_0.pdf

If your not 100 percent with your hoses might as well change them out to give you some peace of mind. It doesn’t cost much

The best diesel rated coolant is final charge by peak. But G05 works in our small diesels perfectly..

cheap too.

I changed out other hoses chasing leaks...and the MB stamped ones are all in the trunk for emergency spares. It was the aftermarket ones that were the problems.