How hot does yours run? - Page 2 - Mercedes-Benz Forum
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post #11 of 18 (permalink) Old 02-28-2018, 04:39 PM
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Revs are normal at that speed. Temp has more to do with coolant flow and air flow to heat exchangers. With AC off and heat on, you should see a goodly decrease in engine temp at the cluster.

I climb mountain passes at 75mph, and temp does not get above 185 on summer days, normally. When the system was not at its best, I did get much higher showings in the 210-redzone. Driving 75-80 for 250 miles did not make for much heat. Slowing down or climbing 6% grades did not show any effect either with a clean system.

This is for a 73, no AC, kept in good kip. YMMV
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post #12 of 18 (permalink) Old 03-01-2018, 08:15 AM
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These cars have electric gauges. Increased resistance can cause a falsely high reading. The 107 often has increased resistance at the instrument cluster where the gauge itself plugs into the circuit board. Use an infrared temp gun to confirm the temp reading.

One sign of a resistance problem which will be seen sometimes is a needle that is not smoothly operating all the time. Sometimes it will "jerk" and change positions.

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Last edited by rick; 03-01-2018 at 08:23 AM.
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post #13 of 18 (permalink) Old 03-01-2018, 12:09 PM
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With factory gearing I think you'd expect about 2500 rpm at 75 mph in high gear, nowhere near 3800 rpm.
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post #14 of 18 (permalink) Old 03-01-2018, 03:13 PM
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post #15 of 18 (permalink) Old 03-01-2018, 05:38 PM
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Quote:
Originally Posted by highleymd View Post
With factory gearing I think you'd expect about 2500 rpm at 75 mph in high gear, nowhere near 3800 rpm.
I am away from home, but on the net, I see 2865rpm at 100kph (62mph) and also 24.5mph at 1000rpm in top gear. There may be differences in the transmissions and rear end of these cars.

using the 62mph number, the rpm at 75mph would be 3466rpm

using the 24.5mph number, the rpm at 75mph would be 3061rpm

Maybe someone can find the official numbers for the OPs car. This is not official, but from http://www.automobile-catalog.com


Last edited by MBGraham; 03-01-2018 at 05:44 PM.
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post #16 of 18 (permalink) Old 06-18-2019, 05:38 PM
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Originally Posted by MBGraham View Post
My 72 Djet runs at just slightly over the 175F mark when driving. maybe 185F? If leftv idling for long period, it may creep up.

Your temperature seems high. At one time my car was like that and I ended up having cracked exhaust manifolds

High temperature can be due to cooling system problems, but also due to timing setting. A retarded timing setting will cause engine to run hot. You could try setting timing so that it is about 27deg BTDC at 3000rpm. This will mean that it will be at about 5deg BTDC at idle with vacuum. This is easy to do with a timing light and perhaps you will run a bit cooler.
Do you disconnect the vacuum lines when setting at 3000RPM? My distributor canister has 2 vacuum lines.
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post #17 of 18 (permalink) Old 06-18-2019, 06:14 PM
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The sticker on the front frame under your hood should tell you whether the vac lines should be connected or disconnected. All the cars are different.My 79 450 SL calls for them being connected.
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post #18 of 18 (permalink) Old 06-19-2019, 06:16 PM
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Do you disconnect the vacuum lines when setting at 3000RPM? My distributor canister has 2 vacuum lines.
Just saw this. If you have a 1977, ignore what I said. Thos timing numbers were for early Djets (72-73)
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