Stuttery Temp Gauge - EDIT: Solution Found

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mrsecman
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Stuttery Temp Gauge - EDIT: Solution Found

Post by mrsecman » Mon 11 Apr, 2016 5:10 pm

All. Over a long period I've been chasing a stuttery temp gauge issue. Here's the lowdown:

Temp gauge normal rise as engine warms or cools, no issues. However, once settled on around 90C it will regularly flick anywhere from 85 to 110, sometimes sitting at either area then settling back down. Happens constantly when car moving (settles somewhat when car not moving/idle).

Also, after initial warm up - say morning warm up - and heading down the road, consistently within first five minutes drive time the needle will move steadily to 105, then settle to 90, and then begin its ongoing stutter/flicker.

Gauge has been changed with known good spares three times - no difference. Temo sender has been replaced with known good sender. No change.

I note that this issue seemed to have started occurring after the water pump was replaced a while back...

Thoughts?
Last edited by mrsecman on Thu 14 Sep, 2017 12:40 am, edited 1 time in total.
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mrsecman

1984 380SEC ('83 Update) - Thistle Green, Top Condition, 2-1/4" Magnaflow Exhaust w/HiFlow Centre Mufflers, Interior Modifications
1994 Honda Accord VTi-S - Daily Runabout - SOLD 2015 (Good New Home) - Thanks for the Service

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TheMadRacoon
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Re: Stuttery Temp Gauge

Post by TheMadRacoon » Mon 11 Apr, 2016 11:46 pm

I've had mine go off-scale suddenly few times and assumed that it was a bad earth. But it's happened only a few times so I haven't chased it.
Emad,
TheMadRacoon
1975 350SLC Astral Silver (725) / Blue (2012, 284,900 km - present.... a real Benz, getting better and better)
1988 190E Deep Blue (900) / Cream (2006, 190,000 km - 2007, ~ 215,000 km .... FSH and still spent big $$$)
1974 280E Reed Green (860) / Bone (1993, 316,700 km - 2004, ~490,000 km and still A1)

CraigB
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Re: Stuttery Temp Gauge

Post by CraigB » Tue 12 Apr, 2016 9:39 am

I'm thinking some sort of voltage stabilisation associated with guages - the OVP relay perhaps?
Craig Baulderstone
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mrsecman
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Re: Stuttery Temp Gauge

Post by mrsecman » Wed 13 Apr, 2016 8:44 pm

CraigB wrote:I'm thinking some sort of voltage stabilisation associated with guages - the OVP relay perhaps?
Yeah wondering about that. Will continue to chase. I've got half a mind to replace the OVP and anything else related anyway, peace of mind. Worth testing though. I just can't see any more that its the sender or gauge given all the testing... Keep you posted.
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mrsecman

1984 380SEC ('83 Update) - Thistle Green, Top Condition, 2-1/4" Magnaflow Exhaust w/HiFlow Centre Mufflers, Interior Modifications
1994 Honda Accord VTi-S - Daily Runabout - SOLD 2015 (Good New Home) - Thanks for the Service

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mrsecman
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Re: Stuttery Temp Gauge - EDIT: Solution Found

Post by mrsecman » Thu 14 Sep, 2017 12:45 am

After some investigation and troubleshooting, we eventually found the cause of this to be the thermostat, with a special modification. That modification is recommended by MB in some cases where the coolant flow needs to be adjusted when cold to shut off properly. What can happen is that the adjuster doesn't fully close or closes off intermittently (even when new) resulting in sudden inflow of colder coolant, which means stutters temperature readings. I'm probably not explaining it very well, but the end result is a new modified thermostat and a temperature reading at gauge of a very consistent 83C with a little fluctuation in traffic or heavy driving up to 96C. Meantime original cluster gauge has been refit, and new temperature sender also installed.

Keep this in mind when encountering this issue in future!
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mrsecman

1984 380SEC ('83 Update) - Thistle Green, Top Condition, 2-1/4" Magnaflow Exhaust w/HiFlow Centre Mufflers, Interior Modifications
1994 Honda Accord VTi-S - Daily Runabout - SOLD 2015 (Good New Home) - Thanks for the Service

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Re: Stuttery Temp Gauge - EDIT: Solution Found

Post by CraigB » Thu 14 Sep, 2017 9:07 pm

Thanks - that's really interesting. I'm trying to picture how you modify it. With any car thermostat i have heard of drilling a small hole in the base plate to help bleed air in the system - I think that is what i was told. I have heard of new thermostats that stick too and why you should boil them up in a saucepan to observe the movement even it is new.

But with that in mind, in hindsight one of those temperature guns (about $70 or so from auto places) would have shown that actual fluctuation at the motor, and know the rest of the sender etc was not the problem.
Craig Baulderstone
Lurch
280s's
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280SL
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mrsecman
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Re: Stuttery Temp Gauge - EDIT: Solution Found

Post by mrsecman » Fri 15 Sep, 2017 12:07 am

Olaf Zaworski over at Horst, Brompton, knows the score with this. Apparently as I say it was an endorsed MB modification to your choice of the thermostat or heater core; either way the effect is to stabilise the flow pressure in a certain part of the cooling system and not result in spots where the coolant flowing past the thermostat resulted in incorrect readings to actual.

In saying all this, I suspect I'm going to need a new radiator soon anyway as it's the original and we may have identified a minor flow issue. Not critical, but I'm anal about everything working properly with this machine (as we all are!), and I'll probably rebuild the aux-fan bearings as well (can be rebuilt much cheaper than replacement).

This is really one of the roadblocks to anyone not enthusiastic about these cars - they are a magnificent machine, but require the care, interest and wallet to do it properly, even if part of the task is DIY which is a lot! :-)
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mrsecman

1984 380SEC ('83 Update) - Thistle Green, Top Condition, 2-1/4" Magnaflow Exhaust w/HiFlow Centre Mufflers, Interior Modifications
1994 Honda Accord VTi-S - Daily Runabout - SOLD 2015 (Good New Home) - Thanks for the Service

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