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post #1 of 7 (permalink) Old 03-07-2012, 06:44 PM Thread Starter
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Running Hot?

Getting my son's 164S road ready has slowed down because the temp guage reads hot. It has a new radiator, new temp switch in the radiator and a new Bosch switch in the thermostat housing. I just installed the Bosch switch this afternoon and ran it for quite a while. After shooting temperatures at different places with the infra red, I'm not convinced it is running hot, but the temp gage is reading 232F, the last small line before the max 250F. The fan comes on and cycles. It drops the temp at the radiator switch about 10F, fans shuts off, the temp goes up 10F, the fan comes back on. Everything looks normal except the gage on the dash.
Has anyone had a gage off that far? It there a quick fix for an inaccurate dash gage.

Red 1991 164S, Black 1991 164S, Red 1987 Milano, 1972 Berlina, 1973 Berlina rebuilding SPICA engine
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post #2 of 7 (permalink) Old 03-07-2012, 08:02 PM
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Mine did the same thing. I think the Alfa temp gauge is incorrectly calibrated. I checked it with the IR gun and the temp gauge was indicating about 20F+ above the IR temp measured on the bottom part of the thermostat housing. I installed a 27 ohm 1/2 watt resistor to the wire and the gauge now reads within about 10F high of the IR gauge.

I also replaced the OEM fan switch with a 85-90 VW Golf 2-speed fan switch. (Wahler, 802 54058 087, 251 959 481 75) Low speed fan 180F // High speed fan 195F. Remember, radiator fan switch is quite a ways from the gauge sending unit, so the gauge may not exactly match when the fan comes on/off. The OEM switch is set to 198F/205F.

The best thing to do would be to put the connected temp sending unit into some heating water and check the gauge reading with an accurate thermometer. I have not done that. Not sure that the IR gun will exactly measure the actual water temp, vice the metal on the outside. I'm sure it's close, however.

John Stewart
74 Spider
91 164S

Last edited by Roadtrip; 08-05-2012 at 01:20 PM.
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post #3 of 7 (permalink) Old 03-07-2012, 08:58 PM Thread Starter
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I get the 2 temp switches/senders confused on the thermostat block. Did I replace the right one? Does the Bosch one operate the dash temp gage, or does the spade one operate it?
I like the idea of checking it in some boiling water.
I did notice when I was heating the car up and checking the gage with the IR, at lower temps, the gage was more accurate at lower temps that higher temps.

Red 1991 164S, Black 1991 164S, Red 1987 Milano, 1972 Berlina, 1973 Berlina rebuilding SPICA engine
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post #4 of 7 (permalink) Old 03-08-2012, 04:36 AM
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Bosch coolant temp sensor (CTS) is for ECU cold start function not temp gauge.

Temp sender small spade for red light and larger one for gauge needle.

Ciao, Alfisto Steve
Virginia Beach, VA
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Alfa Semi-Daily driver: USA model - BB2 1991 164S Black Beauty II ALFISTO [U]

[U] BB1 1991 164L w/S engine and A/T now excess to inventory [U]

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post #5 of 7 (permalink) Old 03-08-2012, 01:30 PM Thread Starter
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Thanks John and Steve. I tested a spare sender I had in boiling water. It read accurate, so I took out the old sender and tested it in boiling water. It was bad. So the spare is in and it is cooling great. I appreciate the help.
Son's car is sitting down on all 4's now. First time in over a year. A glass guy is coming out this afternoon to put a windshield in. We just have to put the drivers outside mirror in, reassemble the door panel and replace the antenna and he's good to go. Hopefully he can get it across the border with minimal problems. I may have to fabricate a tow bar and take it up there with the 164BW

Red 1991 164S, Black 1991 164S, Red 1987 Milano, 1972 Berlina, 1973 Berlina rebuilding SPICA engine
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post #6 of 7 (permalink) Old 03-16-2012, 12:13 PM
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I've found my $29.00 Raytech IR temp gun invaluable in situations like this.
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post #7 of 7 (permalink) Old 03-16-2012, 01:10 PM Thread Starter
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Yes, I used mine to trouble shoot the problem.

Red 1991 164S, Black 1991 164S, Red 1987 Milano, 1972 Berlina, 1973 Berlina rebuilding SPICA engine
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