With the recent cold snap and difficulty in starting I've had my zerostart lower rad hose heater plugged in all night.

One thing I noticed that makes me wonder is the following; the lower hose and upper half of the thermostat warms up considerably, but the lower half of the thermostat housing and hose downstream is noticeably cooler.

Is this normal? Is the thermostat not opening or something? I don't have any driveability issues.

heat rises?

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[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.

What would be the year and model of the subject vehicle?

Because of the nature of the bypass thermostat arrangement on many MB engines, a lower hose heater is not going to be as effective as it would be on a typical domestic vehicle with a conventional thermostat. With a conventional thermostat, there is no obstruction at the downstream end of the lower hose.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Interesting observation.

Looking at cooling circuit below and assuming heater is in line B. And looking at thermostat that is lying on my desk and second picture, it seems that tstat will stay closed unless the temperature gets up to about 80C (when it starts to open). The tstat sensor bulb is on the cold side, so it may be hard for that to get to 80C just by conduction through the metal.

There is a small vent valve which should be at top of tstat to bleed air. Maybe it will let enough hot water through to warm bulb and open tstat?

Once open at 80C, bypass valve will still be open. It would have to close before hot coolant is directed to block. That would be at about 94C - unlikely to get there?

Maybe heating thermostat housing with hot air gun would help get circulation going?

Doesn't seem right. Maybe I have this wrong? Perhaps not reading this thread!

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

Apologies, it is a 1978 300D. The hose heater is indeed at point B in your diagram. So is it useless then?

The lower rad hose heaters work by convection effect, so the heat moves upward through the coolant.

They are not useless, but they aren't a substitute for a working block heater. I would guesstimate they are about as effective as the magnetic heaters applied to the oil pan or block, maybe a bit less.

The other type of heat source, which no one mentions around here, is the silicone pad heaters that you apply to the oil pan exterior. Again not as good as a block heater, but much easier to deal with installation wise.

My 300td has no block heater (from Texas) and I plan to try to get by with an oil pan heat pad, a lower rad hose heater and a battery heating pad. I got behind in my work as the winter hit so right now I got none of the above is installed on the td. Not good.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

Problem is, the thermostat puts a major crimp in the convection theory. Same with conduction. Domestic vehicles typically don't have that problem.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Zach - Have a good look at the coolant diagram. Sure the heat will rise by convection and it will heat the coolant within the rad hose. But it can't get beyond the thermostat which is closed. See my previous post.

These hose heaters may work on other cars, but I can't for the life of me see any way they could get heat into the block on a Benz.

aieeegrunt. Yes, as far as I can see, it is useless other than providing some under hood heat.

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

I did some experimentation and indeed confirmed it is basically useless; I drove around for a while, warmed the car all the way up. As soon as I got home I plugged the heater in.

Went back out two hours later, I could hear the coolant chugging around in the hoses, and the whole of the thermostat housing and the return hose to the rad was quite warm. So it's not warm enough to open the thermostat on it's own, but if the thermo is already open it seems to supply enough heat to keep everything going.

So it seems I will be getting by this winter with a magnetic oil pan heater, a battery warmer and a trouble light. It is to the car's credit that despite my idiocy it kept starting till it spent a week in -20C weather.