Glow Plug Relay Questions - PeachParts Mercedes-Benz Forum

coolerelmo · #1 03-31-2008, 11:51 PM

I have a couple of questions regarding the glow plug relay on my 81 240D. This is due to sometimes the relay doesn't work.

1. I took a look at the fuse on it. It is a metal type of fuse. Is there a newer type of fuse that I should replace it with?

2. If I were to replace it, should I clean the connections again before I install them on the new relay?

3. If I install a new one, is there just the two connections?

Pete Burton · #2 03-31-2008, 11:58 PM

no, only if it;s really nasty, which i doubt, yes. also, that fuse can crack and not look obvious. BTDT

coolerelmo · #3 04-01-2008, 12:05 AM

Quote:

Originally Posted by Pete Burton

no, only if it;s really nasty, which i doubt, yes. also, that fuse can crack and not look obvious. BTDT

Would the relay still work if there was something wrong with the fuse?

xdjio · #4 04-01-2008, 12:37 AM

The strip fuse can (so I hear) be a source of intermittent troubles with this relay. If your strip fuse weren't conducting, your glow system would be dead in the water.

coolerelmo · #5 04-01-2008, 10:37 AM

Quote:

Originally Posted by xdjio

The strip fuse can (so I hear) be a source of intermittent troubles with this relay. If your strip fuse weren't conducting, your glow system would be dead in the water.

Ok, so I should try a new fuse before buying a new relay, right?

xdjio · #6 04-01-2008, 10:46 AM

Oh yes, you should. At the very least, a new fuse will save you the inconvenience of hunting down and testing a relay from a wrecker (or hopefully not buying one new).

barry123400 · #7 04-01-2008, 12:11 PM

Quote:

Originally Posted by coolerelmo

Ok, so I should try a new fuse before buying a new relay, right?

You can inspect your orignal fuse by removing it. Any defect will be obvious as it is only a calibrated strip of metal. Saves hunting for a fuse if not required.
In my opinion though your problem is more likely to be an old tired glow plug relay. Seek out a hulk at a wreckers for a used one or try one of the used parts from our used parts forum. Those relays get tired with time. Just my experience and you would need to substitute the relay anyways before troubleshooting further if the fuse strip is intact.
The above said at some point of developement of the glow plug circuit on 123s the relay light would not come on if certain glow plugs had failed. So quickly check all your glow plugs for continuity. I do not know what year that started in. Not coming on would be a constant in my opinion. Since yours again is intermittent beg, Borrow, or aquire a cheap relay for a test.

duckaroo · #8 05-10-2008, 04:58 PM

I have a 1981 240D and i replaced the relay with a Ford one....eek.....and installed a push button under the dash to warm the glow plugs. Works like a charm.

Stevo · #9 05-10-2008, 06:00 PM

Quote:

Originally Posted by duckaroo

I have a 1981 240D and i replaced the relay with a Ford one....eek.....and installed a push button under the dash to warm the glow plugs. Works like a charm.

If you have a push button switch why the relay?

coolerelmo · #10 05-10-2008, 09:06 PM

It runs allot better when it is cold now. Where is the temp. sensor? Is it in the relay or some where in the engine.

#11 05-10-2008, 09:18 PM

Quote:

Originally Posted by coolerelmo

It runs allot better when it is cold now. Where is the temp. sensor? Is it in the relay or some where in the engine.

The glow plug relay gets an input from a temperature sensor on the engine (coolant temperature).

tangofox007 · #12 05-10-2008, 11:36 PM

Quote:

Originally Posted by Craig

The glow plug relay gets an input from a temperature sensor on the engine (coolant temperature).

According to my information, 1980 was the last year for the coolant temp sensor. Starting with the 1981 models, the sensor is in the relay box and measures ambient air temperature to determine the light duration and length of the glow cycle.