'87 300D Glow. Check My Diagnosis?

[Duncwarw]

First, the dash light went out.

Since I could/can still hear the relay and the dome light dims for about 30 seconds, I figured the glow plug circuit was still working and maybe the bulb was out.

I ran through the checks in the manual, bringing pins 1/3 and no light.
I replaced the bulb and did it again and the light works.
The manual says that means the relay is shot.

BUT, when the relay is closed, I get voltage to the glow plugs.

It's 30F today and the car won't start, even with a shot of starting fluid.

I'm assuming that the glow plugs are bad. Ohming them out, all but 2 0 out, the other two read almost 0.

It's always started a bit hard, but last year it still started at -10F.

Though I suspect I'll need to do stem seals as a couple of cylinders don't really "come online" at first, that's nothing new.

So, I can live without the dash light and I suspect that the light circuit in the relay doesn't really have anything to do with the relay firing the plugs.

Am I right?

[tangofox007]

Originally Posted by Duncwarw

I suspect that the light circuit in the relay doesn't really have anything to do with the relay firing the plugs.

Am I right?

Yes.

[babymog]

You are right, the light circuit is independent of the glow circuit.

Using starting fluid in a glow-plug engine is bad.

[Duncwarw]

Thanks.

Yeah, I know the starting fluid thing is a bad idea. Desperation I guess.
The down-side of living rural is that when you're stranded, you're TRULY stranded.

NAPA is getting me Bosch glow plugs for this afternoon for a good price.
Now all I have to is get a jump start. It's trying (and smoking), I just don't have enough juice to crank for a long enough time to get going.

Thanks again for the quick response, hopefully, I'll get those plugs in without removing the manifold and this will be one more issue behind me.

[babymog]

Use the "juice" to glow it longer, ... but without cranking speed you might be SOL.

[vstech]

even rural areas have electricity... get a good battery charger for sure! winter time is NOT a time to have a weak battery.
heck, even those solar chargers are better than not charging the battery at all.
also, there is a block heater on your motor, be sure and plug it in if you are having trouble starting the car.

[Duncwarw]

Yep, thanks.

I have a semi-permanently installed trickle float charger on it.
I have to get a look underneath to spot that block heater.

The owner's manual says it's there and the original owner never turned in the certificate for the free cable install.

Just got back from picking up the new plugs. LONG drive in the surprise snow.

I have to say, this is the WORST car I've ever owned in the snow, and I've owned a lot of cars......

[micalk]

Originally Posted by Duncwarw

I'm assuming that the glow plugs are bad. Ohming them out, all but 2 0 out, the other two read almost 0.

Am I right?

Probably. Not sure what you mean by "0 out" and "almost 0." The plugs should read about 0.7 ohms. Depending on your meter that may be "zero". They generally will either open up (infinite resistance) or go high resistance (which could be as low as 5 ohms or less). Either way they are bad. If you doubt a glow plug, pull it out of your engine and see what happens when you apply 12V across it. It should glow surprisingly bright red or even orange-yellow. If it doesn't you've got a dud for sure. Replace every one that doesn't glow right. When they are all good, and with all other things being adjusted right, you should start right up. YMMV.

[Duncwarw]

Forgive the shoddy terminology.

When I wrote that I read "0". I meant that I read no resistance.
Like if you touch both probes together.

I'm using a good Fluke auto-ranging multimeter.

Given your 0.7 Ohms figure, I'd say that I probably have only two "good (-ish)" glow plugs (0.5 readings).

With all the snow and no need to venture out again today, I'll get to changing them out tomorrow and report my findings.

Meanwhile, the trickle charger and temporary heater are plugged in.

Thanks for the info.

[micalk]

A "0" ohm GP is a dead short and will blow the 80A fuse in the relay. If you haven't checked it yet, you might want to just pull the fuse for good measure, make sure it is whole and not cracked in the middle, clean the ends and put it back. Couldn't hurt.

[snookwhaler]

I can say that replacing the GP's do make a huge difference. When I first got my current MB Diesel. It had a bit of a rumble on start up and was occasionally hard to start. After lurking around the forum and following a couple DIY's, I found that most of them were bad. I replaced the bad ones and the rest is history.

Fast forward to this past winter. There were several nights when the temps. dipped down into the teens and too many nights in the 20's (for Florida). With the glow system working properly my cold starts were clean, smooth and uneventful. The engine will light off immediately with no issues now.

I remember reading that they can be a bit of a PITA on your particular car. Just take your time. I know it is difficult to do in the cold...

[scottmcphee]

Originally Posted by Duncwarw

Yep, thanks.

I have to say, this is the WORST car I've ever owned in the snow, and I've owned a lot of cars......

a bit OT, but... you need really good snow tires on this car. But once they're on there it's not so bad in the snow. I've got a set of deep tread studded tires ready to go.

[babymog]

I don't agree it's bad in the snow either, I drove several of my 124s regularly in the winter snow when I lived in Michigan. Old/bad tires don't cut it, but that's true on any car, and yes good snow/ice tires make them quite good in snow as does a 50# bag of sand over the axle.

Chances are the tires are in the same condition as the glow-plugs?

[Duncwarw]

Funny. No the tires are new.
Come to that, so are the glow plugs!

Sorry for the delayed response but I didn't get a notification this time.

Just to close this out, I replaced the glow plugs (not a pleasant task) and blew the 80A "fuse". My error, of course. I corrected that (81 cents) and it's a different car. Next morning, in the low 30s, it started faster than it ever has. I wonder what kind of tool people use to get that manifold off? The manual says a swivel but I had a hell of a time with some bolts.

I put the old GPs on the ohm meter and they are all over the place.
The connection clearly could be better, but they all were treated the same way. Pics below.

As for the tires, I'll probably invest in studded snows. I've never had them before but there are an awful lot of people up here who use them and swear by them.

Anyway, thanks all for the good info, as usual.

[micalk]

Good Job!

Is the dash light working again?