Car Talk Blunder

[shertex]

I love Car Talk....listen faithfully evey week. My ears perked up when a woman called in this week with an issue with her 93 300D. Her problem? No heat at idle. I thought, "Oh, this is an easy one." They went on to suggest three possibilities: low coolant, air in the cooling system, or bad water pump. They made no mention of the most likely source of the problem: a bad auxiliary water pump.

So, I will continue to listen every week....but now with a bit more skepticism as to their diagnostic abilities.

[t walgamuth]

Their diagnosis was logical in a general sense but they apparently do not have much experience with a benz so did not know about the specific design of the benz system.

They are great entertainment!

I listen occasionally and often wonder if the calls are done live or are pre-culled and pre-researched.

[shertex]

Originally Posted by t walgamuth

Their diagnosis was logical in a general sense but they apparently do not have much experience with a benz so did not know about the specific design of the benz system.

But isn't the use of an AWP common in other diesel cars? I wouldn't think it's unique to MB's.

[vstech]

I have noticed several omissions of logic and some mistakes from them in my opinion on several occasions.
they are fun to listen to though.

[t walgamuth]

Originally Posted by shertex

But isn't the use of an AWP common in other diesel cars? I wouldn't think it's unique to MB's.

You may be right. I have not owned any other diesel powered cars besides benz.

[engatwork]

I heard that yesterday too. That was not the first diesel MB call in that they misdiagnosed.

[funola]

Originally Posted by shertex

But isn't the use of an AWP common in other diesel cars? I wouldn't think it's unique to MB's.

My 45 mpg 92 VW Jetta TD does not have an AWP and gets great heat at idle. Maybe it has something to do with its water pump and thermostat being located at the bottom of the block, whereas the W123 diesel's is higher up near the cyl head? Come to think of it, my 83 300D's AWP was not working and I was getting decent heat at idle. Maybe it's a problem only on the newest MB diesels?

[kerry]

I suspect that perhaps it is the bypass nature of MB cooling systems that warrants the auxiliary water pump. I heard that diagnosis but missed the early part about it being an MB. The misdiagnosis a lot. Just like the rest of us

[engatwork]

Aren't the characteristics of what she described the same as when the monovalve goes bad too or is it the other way around?

[funola]

Originally Posted by engatwork

Aren't the characteristics of what she described the same as when the monovalve goes bad too or is it the other way around?

Wouldn't the monovalve, if closed, result in no heat at all times?

[barry123400]

Originally Posted by funola

My 45 mpg 92 VW Jetta TD does not have an AWP and gets great heat at idle. Maybe it has something to do with its water pump and thermostat being located at the bottom of the block, whereas the W123 diesel's is higher up near the cyl head? Come to think of it, my 83 300D's AWP was not working and I was getting decent heat at idle. Maybe it's a problem only on the newest MB diesels?

This engine series was one built by volkswagon under licence from mercedes I always thought. There as you mention is no additional coolant circulation pump.

The heater is unbelieveably good compared to most diesel heaters in my experience. It was a shame mercedes did not use simular design in the 123s. I noticed you live where there is some corrosive factor. The thin wall coolant tranfer tube runing across the block should be coated with a thin coating of heavy based grease. It does not seem to take a lot otherwise for the tube to perforate. So simple to eliminate as a possibility.

The tdi volkswagon series abandon this heater feed design as well and had a pretty lousy heater in comparison to their engines up till then. Milage and principally rust have taken the vast majority of volkswagons earlier diesels prior to the tdi off the road here now. You ocassionaly still see the odd one.

That engine series in my humble opinion was one of the best ever marketed in a car from the aspect of low service requirements and durability except for the abortion of a rubber timing belt. Even back then it was quick and cheap to change compared to later belt setups. I am happy to see manufacturers gravitating back to timing chains over time now.

[shertex]

Originally Posted by engatwork

Aren't the characteristics of what she described the same as when the monovalve goes bad too or is it the other way around?

I'm pretty sure excellent heat all the time EXCEPT at idle points to a failed AWP....certainly has been my experience.

[Stevo]

I listen to those guys every week, love em, but they are definitely down on old MBs, as far as they are concerned any car with more than 150K is ready for the crusher So they obliviously don't know or care much for old diesel MBs.

[Skippy]

Am I the only one who considers poor heat at idle to be a non-issue?

[tankowner]

They probably get it wrong about as often as they get it right, but they are also simply going off the descriptions of the owners, which isn't always the best. That is actually the basis of their "Stump the Chump" segment where someone calls in with a problem that they attempt to diagnose. At some later point the original caller is called back to determine if they were right or wrong with their diagnosis. It's all part of the fun. Great radio show and funny, too. To their credit, I doubt they get many old diesel MBs in their shop, but in general these guys are pretty knowledgeable across a wide spectrum of automobiles.