After a light freeze overnight, my block heater was plugged in from 0500 to 0915. The temp gauge barely came up (see pic). A couple days before that, I had it plugged in for about 2 hours and the gauge didn't move at all; it was firmly below the C.

I have measured the amp draw with a clamp meter and it's drawing 7 amps, which is 840 watts. I thought these were supposed to be 1000 watts?

I don't have trouble getting the truck started, even when it's quite a bit colder. But I have to coast downhill all the way through the town, and the engine does NOT warm up. Also the frost on the windshield tends to be very stubborn and won't just scrape off till I apply some heat or direct sunlight, and idling the engine until I can see well enough for safety takes an eternity.

 

Mt temp gauge doesn't move at all after being plugged in for 3 to 4 hours every night, but this is well below freezing. Starts just fine after being plugged in though. And, no heat in the cab for me until the engine is warmed up. I'd only be concerned if you had hard starts after plugging in.

I was on a job for awhile that was a 9% grade for 3 miles, kind of hard to warm an engine up when injectors aren't firing!

 

My 2002 starts fine sub zero F plugged in for 2 hrs. I also shield radiator if expected high is below freezing. Works for me!
Still takes about 15 minutes drive time @ 1500 RPM to come up to normal operating temp from cold (below 32F) start.

 

4 hrs isn't long enough to get the full effect from the block heater and 840 watts sounds about right. The stock ones I thought were either 8 or 900. I know I've seen some 1000+ watt bigger ones that will fit on ebay, but it sounds like yours is okay. Messy job replacing those (coolant everywhere) and it could be seized in there bad enough to mangle the threads on the housing. When I pulled my oil cooler a few weeks ago to reseal it I purposely left the heater element alone.

 

What about an extra heater on the other side of the engine? Freeze plug heaters are available for under $50.00 right now.

 

Yep, 900 watts is the recent OEM I installed. I had a 1500 watt unit before the recent one but due to their electrode length they are tricky to install. The movement of the gauge with the OEM unit will be little to none all dependent on ambient temps. If it’s really cold set the timer for 5 hours.
Sounds like you’re ok as others mentioned.

 

From my understanding the OEM block heaters are rated at 1,000 watts. If that rating is at 120 volts that means the resistance is 14.45 ohms and using Ohm's law we get 8.33 amps. If the OP is only measuring 7 amps it is likely the voltage is low from a long circuit run or extension cord. A heating element rated at 1,000 watts @ 120 volts but only drawing 7 amps indicates that the supply voltage at the load is only 101 volts. It's not a problem with the element, nor will it hurt the element, it will just produce less heat. Some equipment is rated at 115 volts (all motors) but at what voltage they rated the 1,000 watt heating element at we don't know unless someone can read the printing on a new one, but 115 or 120 it doesn't make much difference. Just out of curiosity I will go check mine today and measure resistance, current and volts.

 

Here it is, you can just make out the 1,000W and 120VAC printed on the right side in the 6th pic https://www.ebay.com/itm/321937565846 Under ideal conditions at 120 volts it will draw 8.33 amps, but as I mentioned when the voltage drops (on a resistive load), so does the current(amps) and the power(watts). (An inductive (motor) load is different and when voltage drops at the load current will increase and power will remain the same, and damage can occur) while on the resistive load as voltage drops so will current and power and there will be no damage to the unit, in fact it will last longer just like 130 volt incandescent bulbs last longer. at 120 volts, but glow slightly dimmer.

 

Checked mine, I measured just under 8 amps and 117.6 volts at the load, resistance was 14.8 cold. Which means it is producing 934 watts of heat. The OP states his amps are only 7 which, if his resistance is the same as mine, is only producing 725 watts. See pics. My suggestion, check voltage at the load and verify that the 7 amps is accurate, even a half amp can make a sizeable difference. Also check the resistance of your element. If voltage is low at the load (while energized) look at things like undersized extension cord or outlet being a long ways from the service, or something else on the same circuit taking power. If the circuit/cord is long you are adding resistance and paying for electricity that is being wasted in heat produced along the circuit and cord instead of in the element. It is important to measure at the load, if you measure at the beginning of the circuit you will be measuring the total draw of the circuit + the load with no way to tell how much is making it to the load.

Mine


OP's

 

The plug end and pigtail fails way more often than the heater. Check resistance between prongs on the plug.

Your truck holds 9 gallons of coolant. 800# of cold iron and that much coolant take a while to warm up.

 

bigb56 has you on the correct path. I will throw in as well.

First is the gauge on the dash is only slightly better than an idiot light, but does give some information. If you want a better coolant temperature get an after market gauge. You could also use something such as FORScan to monitor Oil temperature prior to and after start. The oil temperature will experience a slight drop, then rise after start but will usually be near 100 degrees prior to start if it was plugged in for a few hours. Understanding the system will help you understand why the temperatures change the way they do.

Most of the stock block heaters should read in the (((neighborhood))) of 10-15 ohms.

If you are showing about 7 amps draw you are in the correct neighborhood. Many items affect the effectiveness of the system. Look at your house for starters.
What wire size is from the breaker to the outlet you are using?
How far is the run to the outlet?
How many other items are on the same circuit?
What size extension cord are you using?
How long is the cord you are using?
Are all connections in the system tight and clean? Darn hard to check when it comes to the house side unless you tear stuff apart.

You should be using at least a 12 gauge extension cord. If the house is not 12 gauge wired you are also reducing the effectiveness of the system. Even if everything is 12 gauge wiring, the further you are from the main feed the more voltage loss you will have and the more heat you will have in the wires.

bigb56 and I got a bit geeky on you, however maybe you got some good information and a better understanding.

 

Solution:


I seem to be using this picture a lot lately.

 

Recently I tried it with a generator and about a three foot extension cord, and got about the same amp draw. So the house wiring is not (much of) a factor. I'll check the cord in the truck, see if I get the same resistance at the heater vs measured through the cord. I've replaced the male end of the cord before, and it likely has corrosion again at this point. I see the OEM cords are pretty expensive--a lot more than the heater itself--so if it comes down to replacing the cord I just won't bother about it.

Do y'all tend to have trouble scraping ice off your windshields? That's really my biggest issue. My windshield just seems very "sticky" and hard to scrape off, and there are times I have to idle the engine for 20 minutes or so before I can safely drive. I wonder if an older windshield is more "sticky" than new glass without tiny scratches and pits.

 

I've done similar things to thaw out the water tank on an RV.

 

I got rid of my cord and installed a Marinco power inlet in the bumper. As far as the windshield, when I used to park outside I just put a cover over it at night, even an old floor mat or some carpet will work. Although not a lot of frost in the part of Arizona I'm in.