LS MT125 Rough Cold Start - Glow Plug Issue?

[mslisaj]

This is the third winter with my MT125 and we've had some cold mornings lately. A couple of weeks ago I did my usual first/cold start procedure - glow plugs for about 8 seconds and fire it up. This one morning I thought the engine was literally going to jump out of the chassis. It hammered and banged and carried on like it was going to throw a rod. Finally after about 30 seconds it smoothed out and ran just fine. I immediately thought "I didn't put in the winter fuel additive" and while it was warming up I treated the fuel. Well I'm not too sure this made a big difference but I don't remember this engine running so extremely rough initially cold on the first start of the day. It does fire right up without hesitation though but it makes me think that maybe a single glow plug has died and there is a dead cylinder for this initial run period. I don't have a dealer close by to ask about this so I come to the experts here. Upon going through this with the starts lately I realized that most of the banging noise is coming from hood and engine cowl as I can apply pressure to those components with my hands and all the angry noise goes away but the engine sure runs rough for this first 20 - 30 seconds; and rougher then I usually remembered it.

Any thoughts?

 

[Roadworthy]

You can disconnect the wires from the glow plugs and measure their individual resistances. Bear in mind that with the low resistance of a glow plug you should note the resistance of the meter leads, too. Of course if one of the glow plugs reads open you've found your culprit. You could also check the voltage at each glow plug when they're activated. If you have a defective lead one may not be getting power. Glow plugs don't normally get "weak". They're a heating element usually being good or bad.

 

[Diggin It]

A couple of weeks ago I did my usual first/cold start procedure - glow plugs for about 8 seconds and fire it up.

Any thoughts?

I do 10-15 seconds on a 40 degree morning, longer if colder. Under 20 degrees, I might go 30 seconds IF I decide to go outside that day, which I often don't.

 

[jaydee325]

Just out of curiosity, does this tractor not employ a timer for the glow plugs? My R3039H does. You turn the key on, wait for the glow plug light on the dash to go out (there is also an audible click from the associated relay). Once the light goes out, move the key switch to start.

Since this is a new development, I'd do an open test as described above and go from there.

 

[Underdog57]

I cycle the glow plugs twice when it's cold out, much better!

 

[mslisaj]

Okay gentlemen, thank you all for taking your time to help out with your suggestions or ideas. I'll try and address all of you here. On the gentleman that asked if there was a timer the answer is no. You turn the key to the left, heat the plugs and then to the right to start.
For the gentleman that suggested a test procedure I will check that out as while I have been a mechanic all my professional life I have no real diesel experience. I of course understand their function and operation and the glow plug test is a good one and I'll address that.
Now to the gentleman that holds his plugs on longer depending on how cold it is, it's been awhile since I have had my owners manual out but I think it recommended something like 8 seconds. But the 10 seconds sounds resonable and on a 40 degree morning I don't really have an issue. But this machine has been cold soaked down to 15 degrees lately and maybe the 8 second on time is just not enough. I'll give a longer on time and report back.
Again as I mentioned I don't have a lot of experience operating a diesel engine and I get what the glow plugs do but I have been hesitant to hold them on longer fearing damage. But it's certainly easy enough to try and I'll report back.

Again gentlemen thank you for your time and wish me luck!

Lisa

 

[Diggin It]

At 15 degrees, I stay inside and sip on coffee or something similar. If it was life and death to go outside and do tractor stuff, I might do 15 on, 5 off, 15 on, start.

 

[LS Tractor Owner]

Hi Lisa... been a while... Anyway, you just need to hold the plugs on longer... when I had my 125, I would do at least 25-30 seconds when it is that cold!
It will still be a little rough, but not like you described. I really believe that is your only problem.... just didn't get them hot enough initially.

My son has an 'old school' Cummins diesel in his truck.... no glow plugs.... the other morning it was around 12 degrees overnight. When he started it up in the morning, I thought an old steam engine was coming down the drive.... CHUUGG.....CHUUGG...CHUG..CHUG..CHUG. Then it took 20 minutes to barely move the needle off cold.

 

[mslisaj]

Well I think you guys are on to something. I just got down my owners manual and it says for "cold" starting 4 seconds. I agree that's not enough so I was doing 8 seconds which was not enough. Now last evening it was about 35 in the shop and I went out there and heald the glow plugs on for 20 seconds and it fired right up and ran relatively smooth. Last night it got down to 25 and I just tried to start it with a 25 second on time and it started and hammered around a little bit but it was better. Next I'm going to try the 15 on 5 off and 15 on and start. After seeing it work last night I think this is the key. I'll keep you guys in the loop on what I discover and it's funny the book only says 4 seconds.

 

[the old grind]

I'd bet the manual means just at room temp 'cold'. I'm thinking of adding a manual switch to the relay on two machines. The CUT only has glow when cranking. The Mechron switches plugs off too soon and a coolant temp cutout makes it hard to start after a brief shutdown ... esp in 'seasonably cold' temps.

I throw blankets over my 'good', indoor-kept tractor and put an electric heater under it for an hour before starting when below 20ｰ. Below 15ｰ I don't start CUTs. It takes too long to warm up the hydraulic oil anyway.