How hot should your coolant be with a Block heater?
 

How hot should your coolant be with a Block heater? I left mine on my 85 300D all night and I thought when I started the car it would be piping hot with heat coming out of the vents and the temperature gauge well above 40 degrees. Boy I was disappointed!! Didn't feel any heat and the temperature gauge looked the same as if there was no heater. I am pretty sure the Heater is a good unit....

Does anyone have a block heater where the temp gauge reads above 40 when the car is started and there is heat already?

I used mine one time when I stayed in Vail it was below zero and I only plugged it in for about 3 hours and there was heat from the vents when I started the car. It is the stock block heater in the side of the engine.

That sounds about like mine. If it's very cold (when I use it) the temperature gauge is still sitting at 40C in the morning. It gives me cabin heat in about 30-60 seconds, but not immediately. The top of the valve cover only feeds luke warm, but definitely warmer that the air temperature. AFAIK, that's how they are supposed to work.

with my previous engine, the block heater would JUST move the temp gage, but still a little below 40C. But it hasn't gotten cold enough for me to use the heater in the current engine, so I really don't know.

I agree..something just at or slightly below 40C...from my experience...

How hot your block heater heats the engine is completely dependent on the outside temperature. It will put out 400W, and that power will create a temperature rise proportional to the ambient conditions. This morning was 10F, my car started as it would normally start at about 40F, so I would estimate you get a 30 degree rise from ambient. This rise will be somewhat constant over the temperature range.

Mine was sitting at about 42C the other day, after the heater had run for about eight hours. It was just below 0C outside at the time. The car was in a open garage (no vehicle door yet).

This morning the heater had been running for about four hours and it was about -6C out. The needle was sitting at the bottom, as usual, but the engine warmed up much quicker than it would have.

My 81 300SD is plugged in every night with temps of 10-20 degrees. My timer kicks in 4 hours before I start it. The temp needle is always just below the 40 line. It starts easily and heats up quickly.

My hose heater results in a quick start in any temps I've faced so far,

As for how hot it makes it, gauge sits just above 40C when I put in the key, it makes the radiator/hoses/thermostat HOT (cannot touch them HOT) The block/valve cover get warm enough to not make your hand cold if you put it on it for a while.....and the car heats up within less than a mile to near operating temp. For 375 watt hose heater I am very impressed/pleased with its performance, even in 2F so far! :D

Keep in mind that 40*C is just over 100*F. How much warmer would you want the engine block to be on startup? I wouldn't think it too wise for the block heater to raise it much warmer than that.

I'f this is true, then why does everyone report startup temps hovering around 40*C? This is certainly a testable hypothesis.
Iv'e often wondered how the car might benefit, in terms of longevity, by using the block heater in all seasons.

It most certainly is testable. Couldn't have anything to do with the fact that the temperature gauges all start at 40C could it?

A block heater is just that. There is no thermostat, and there is no extra power to compensate for the cold. Simple thermodynamics dictates the block temperature will dissipate 400W to the air -- since the thermal resistance does not change, and heat transfer is dependent on the temperature difference between the block and the air, the block will be a constant number of degrees above ambient. I estimated it was a 30F rise, but it might be 40F... Believe me, it doesn't melt the snow off the hood -- that doesn't even melt off after driving for 30 minutes.

My block heater does not warm the engine to 40C when it is 0F out, like this morning. But it starts nice, and the gauge lifts off 40C after about a mile of driving. I use it whenever it's cold enough to frost, which is every day now for the last 4 weeks.

I would think the only benefits of year-round block heater use would be less carbon buildup/slightly better MPG on short trips-I try hard not to ever drive mine less than 3 miles a day (on the days I can drive it). Old 300D is exactly right-ambient temps(and WIND) would directly affect how warm the heater would get-mine is usually around 40 C in light wind/0-10F, after 4 hrs on-longer times don't make any real difference. Gotta love that Delvac 1-starts great now-even down below 15F!!