Living in Orlando Fla. I don't have an issue with 35 degress or lower, but I have had to start using my block heater due to a rough cold start in the A.M.. Truck has 250,000 miles on it!Runs smooth after it gets to operating temperature, if I don't use the heater, but the heater makes it ready right out if the box.

 

I have new GPs and the GPR but still struggled when unplugged. What changed and eased cold starting was 5-40 synthetic oil even when it was in the single digits unplugged. Still not good as my W123 300D Mercedes, specially when I changed the batteries. My MB (it has over 300K miles )starts even before the WTS light turns off when it is 10 or lower. I am going after batteries next but that would be like a $300 expense. We did some winter camping when we had a cold spell here in Northern NM (it was 0 at one point) and me and my wife just started the truck and let it idle for 5 minutes at 900 RPM at 9 PM, 12 AM and 4AM when the oil was still dino 15-40. We also carried a 800 amp battery pack with us.

The 5-40 synthetic seem to help with the rough idle and cackle as well. But I know guys here who don't buy the syn myth but they probably have new injectors or keep their strokes in tip top shape and they could probably use lard and get away with it.

 

Checked relay and it tested good so went to the glow plugs next. Found 4 not working one which was unplugged and the others only had like 2.4 resistance when tested. It was 29 degrees yesterday and truck started perfectly first cycle one changing all the glow plugs. just an fyi changing glow plugs is not and easy task make sure you have a day to spare.

 

Just changed out all 8 glow plugs and seemed like it fixed my cold start issue. Did not plug in the block heater last nite and it did not want to start normal. Plugged it in for a few hours and it fired right off. I live in Orlando, Fla. and it was not near 35 degrees last night. Just put fresh oil in also, 15w40 Rotella Diesel engine. Still runs rough during warm up, then smooths out for the rest of the day.

 

Check the relay.

You should not have any issues starting at 35*.

 

Did you check the relay?????? Mine was good so i checked the glow plugs second. There is 2 relays on the top of the engine the one closest to the cab is the gp relay when you turn the key on you should have 11+ volts to all the legs and none on the right leg when the key is off.

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FYI need to make sure you batteries are good before you look at relay or gp's. Looming at the simple things first will save you money and time. Its not always a huge issue its usually something small causing a huge problem.

 

I have just replaced all 8 of the glow plugs because I was experiencing a rough idle at cold start, sometimes did not want to start. Cold weather is not an issue here in Florida. Check the GPR with a multimeter just now and I have 12.65v at the large terminals with the key off. When the key is turned on, I now am testing the smaller wire terminals and watch the meter climb to roughly the same, 12.56v. Am I doing this right? Seems like the GPR is OK also. Just changed the motor oil with 14 quarts of Rotella 15w40 for diesel engines. After the truck warms up it seems to shift into a different power mode and smooths right out. Never have a problem the rest of the day.