Since the factory block heater is completely inaccessible unless the car is disassembled, I'm thinking of the next best thing is probably a heater within the lower radiator hose. Has anyone done this and has it worked. What hose diameter is needed?

Is your heating element defective? It's often just the cord.

I've used an inline heater on a 220D, it worked eh', it wasn't as effective as the OE because the OE element puts the heat exactly where it is most effective i.e., around the water jackets.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

It could be the cord. But, reaching the element where the cord connects is very very difficult!!!
Who know of the best aftermarket solution?

The inline work just fine but take longer to heat up.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Replacing the cord isn't difficult, it plugs on to the element under the intake manifold. Been there, done it.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Did you get access from underneath?

Yes from underneath. It wasn't difficult at all but, prepare to get dirty unless it is a very clean engine bay. It involved undoing a few tie wraps, unplugging the cord from the heating element then reversing that for install. The old cords are often in very bad condition.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Yeah I got access to my block heater when I changed freeze plugs on that side of the engine. I had the turbo and intake manifold out. I was surprised at how small it was. I was tempted to remove it since I live in sunny Southern California. The cord looks easy to damage. I can see how 90% of the failures are the cord.

ETA - yeah, look at the bend in that wire. I bet mine is fatigued at that point. I’ve never tested it.

__________________
79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles

I don't have a lift , but seem to recall getting at the heater element without too much of a problem. What I do recall, is that there were two types of heaters. They had different sockets for the cable plug. My engine was changed at one point and the '85 version of the cable would not fit in the socket of the ~'82 vintage engine. I seem to recall that one type was hard to source.

I at one time had one of the in-line hose heaters on my 350SL. It worked, but I abandoned it when I changed the hoses. Car is not winter driven.

For the 300D, I used a magnetic heater that can be attached to the sump. It served me for many years when the car had to run every morning so I could get to work! My car was in an unheated garage, but the shelter no doubt helped.

Before anything else, I would make sure valves are properly adjusted, compression is good and glow plugs are all working. And, battery is fully charged and perhaps left on charge overnight. Some use a battery warmer. Then car will start in most conditions.

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5

I think you are correct here. The cord appears not to have power all the way to the heating element. I'll replace the cord and I suspect that the element will work. I just need to order the correct one on Amazon now.

Yet it could be the electrical contact ends simply need to be cleaned.

There is all kinds of lower radiator hose coolant heaters. Which ones are top of the line or junk I cannot say.

__________________
84 300D, 82 Volvo 244Gl Diesel

Well, as Sugar Bear said, it was the cord and not the block heater. If anyone has a non working block heater, check the cord first. They're cheap. But, there are two types of cord. Make sure you get the correct one for your car.

Glad you got it. They work really well producing about 600W??? IIRC.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Glad you found the cord to be the issue. I’ve not found a failed heater on any of my diesels (knocking on wood). You should still ensure all maintenance items have been handled. That’s important.

And if you truly live in a frigid place, a magnetic oil pan heater is a great idea.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)