I have talked with two 300D owners who told me that the one thing to keep an eye on with the older models are the two oil cooler hoses. One guy said he burned up the engine while driving hard on a long trip when the hose blew and it was too late by the time he realized it. The hoses on my 300D are looking greasy where it connects to the cooler, maybe I should consider changing them out? Anybody had this happen before?
Phill
81 300D
260,000 mi

Phill,

I own a 88 300e and a 83 300cd. Although I have not replaced the oil cooler hoses on either as of yet. I have replaced the tranny cooler lines on the E. The hoses were kinda wet and spongy looking. Parts are inexpensive (purchased from the FASTLANE) and it is definately a DIY job. One caution to pass on is possiblity of aluminum fittings on the radiator side of the lines, which could be stripped easily.

Marks88

I have personally never seen an oil cooler hose fail. But, given that these cars are now becoming around twenty years old, it certainly wouldn't hurt for us to keep our eyes on them. I'm glad you mentioned this.

Have a great day,

Hi Phil,

It is nice to hear from you again.

About 30% of used diesels with 617 engine I test drove in the past had leaking or cracking hoses. The leak is usually from the joint (oil cooler side) where the rubber and the metal pipe met. I have heard stories like yours resulting in engine damage. Another reason causing hose problem is motor mount failure. As a result, the power steering belt cuts thru one of the hoses. It is not easy changing these hoses. I change them whenever I see cracks or leak. I do not want to take that chance burning up the engine.

As for the transmission flex hose, if it does not have coil spring around it, I change it with the updated hose (coil spring around the hose) regardless the condition of the hose. If the car already has the updated hoses, I check for cracks or leaks. Replacing the tranny flex hose is very easy. When order the tranny flex hoses, it is better to measure the length first. For some reasons, the tranny flex hose called for by the part book is too short for some cars.

David

Hi David, so you remember me huh? Nice to hear from you too, you've always been extra helpful.

Very good info here. The lower hose does seem to leak some, it has oily greasy build-up on it. I've put about 20,000 hard mileage on the old gal since I last posted hear. She's running fine, and that oil has been on there since then, right where the rubber and metal meet as you said.. i'm afraid I'd better do something before I regret it. Everytime I take a long trip I keep my eyes glued on that oil pressure guage.

Also, you mentioned motor mounts. They are flat. Need replaced big-time, but it doesn't appear the belts are interferring with any hoses.

Thanks
Phil

Hi Phill,

I hope you get your brake problem fixed soon and keep on dieseling.

The motor mount failure is not the only factor causing the belt to cut the hose. Each car is different. The tension of the PS belt, the position of the PS pump, and position of the AC compression are also the factors changing the gap between the PS belt and the oil hose.

I would change the oil hoses if they leak since the oil pressure is very high at highway speed. Are you trying to change the oil hoses yourself? To change the hoses, you need to unbolt the motor mount. It is the right time to change the motor mount too.

David

David,
I plan to change them myself, but you mentioned it being a tough job. I'm not a man of great patients or time. ha.

I actually have quite a bit of small jobs needing worked on and I don't have the most time in the world. When I go to the mechanic in the morning re brakes, I may just let him do them while he's got it.

other jobs needed: AC has quit blowing cold air for some reason (new pump was installed year ago) I'm figuring needs freon ; it's also over due for valve adjust.; and park (pawl?) is loose and I've never got a chance to fix that yet. Oh yeah, glow plugs still don't work half the time either, (think i mentioned that last year) which has not been a problem over the summer. Kind of wierd, but the plugs work when it's warm, but won't come on when it's cool/cold! go figure.

Till later,
Phil

Phil,

If you plan to do the job, here are the problems you may face:

(1) You may not be able to unbolt the 6 mm allen bolt (from the bottom up) mounting the motor mount. It is very tight. If you strip the allen head, it is very very hard to unbolt it since it is inside a cave.

(2) You may not have room and/or the right size tools to remove the hose nut at the oil filter housing.

(3) The oil cooler connectors are very soft. They may break during removal or installation of the hose connectors.

(4) The left side of the engine has to come up few inches in order to snake the new hoses in. It is not easy to snake in the hoses right the first time. Once the hoses are snaked in but in a wrong angle, there is no room to move the hoses around to get it right.

To make the matter worse, the black engine oil is all over the place.

I hope I do not scare you.

David

hello from mike webb foreign car repair , we see those hoses broken ussually when they get mixed up with the belts and or pulleys , we have a 300sd in the shop right now that has 90PSI of oil pressure @ 3k rpm ! and no problems with the oil cooler hoses , but it was enough pressure to cause the sending unit to fail ..... thats about 6BAR ! in system designed for 3BAR max .... the hoses in this car are about 6 months old , now i gotta find out why the oil pressure is so high ??? even with a new mercedes oil pump that has the pressure regulator incorperated in the housing , the pressure @ idle actually went up ! from 30PSI to 60PSI !!!

Maybe something is plugged Mike. Has the owner changed anything recently that could have broken any "crud" loose that has found its way into the oil passages? How in the world did the owner know that the pressure was too high because once it gets to 3 bar you don't know how much higher it is.

__________________
Jim

hell from mike webb , the car was brought in for no oil pressure reading on the gauge , when we get one that has no oil pressure we check the oil level , if its ok we connect oil pressure gauges to the port where the oil pressure sending unit goes , when we did that we saw instead of low pressure very high pressure , so thinking the cause must be a binding oil pressure relief valve we replaced to oil pump , ha , the oil pressure is now higher than it was , ?? we have since tryed running it with no oil filter in the housing in case the oil filter screen was too tight a mesh , same same , i dont see a bypass valve for the oil filter which if it stuck closed may theoreticly cause this ??? mod does not show an oil flow chart ??? the very high pressure must have damaged the original sending unit causing the low reading when the car was brought to us ....

Mike,

I checked the 126CD and the relief valve in the pump is not supposed to move until the pressure is gteater than 7 bar. 3 bar at 3000rpm is the minimium acceptable presssure for reliable engine performance. Both of my SDs peg the 3 bar gauge at anything over idle even when hot. I hope this helps.

Bob D.

hmm , this is good to know , thinking about it most of the sd s that we see do the same thing , this is the 1st one ive actually had to measure , but i dont think any automotive engineers operate their engines @ 90psi oil pressure as a normal operateing spec ? i have measured many others and this is about the highest pressure ive seen in an engine oil system .... the local machine shop also thinks this is way too high , but ?

I doubt if you will see very many owners on here that have actually "measured" the oil pressure because like h2odiesel said - most of them peg the needle as soon as you get above about 1000 rpm. It does sound high but if the engine is running good and nothing seems amiss while driving I would be hard pressed to be too worried about it. Another thing that comes to mind too is what weight oil are you running (I sure hope this does not start another oil thread ) AND are you letting it get good and hot prior to taking a reading. I would think that once that engine gets good and hot that oil pressure will drop - especially at idle. If the engine is running good try it and see what happens.

__________________
Jim

to h20 diesel and anyone else; re reading your post i see that according to the benz 126 cd the oil pressure relief does not begin to open until system presure reaches 7 bar ? thats 105 psi ? assumeing thats not a typo graphical error then i am barking up the wrong tree here and there is no problem with this system at all , it just had a bad oil pressure sending unit ..... and i am chaseing my tail, incorrectly assumeing this system to be the same as other systems i have worked on , and assumeing benz engineers think the masses dont need to know their actual oil pressure as long as its above 3 bar dont worry about it , they could have used a vw type system with 2 oil pressure switches 1 for high rpm and pressure 1 for low rpm and pressure ,
well ive barked up the wrong tree before , its better that i learn my mistake now before i waste more time chaseing down a non-problem , thanks for the tip , please confirm its not a typo thanks again mike webb