coolant temp sensor - The 1947 - Present Chevrolet & GMC Truck Message Board Network

70c-10 · 10-13-2010, 01:43 AM

Does a 1988 Chevy c1500 have two coolant temp sensors, or just one (ie - one for the computer and a separate one for the temp gauge)?

My temp gauge seems to be working ok, but results from a failed smog test show that the engine is running rich. I have already replaced the o2 sensor. I am wondering if I should replace coolant temp sensor too. If the temp gauge and the computer use the same sensor, is it possible for it to work for the gauge, but not allow the engine to enter a closed loop?

BigBlocksRule · 10-13-2010, 03:02 AM

Gauge sensor is in the driver's side cylinder head, intake coolant temp sensor is on the front of the intake. It could be going bad, but will definitely be noticeable if it's out - it'll run pig rich and rough, the engine will think that the coolant is -50* or so.

70c-10 · 10-13-2010, 03:04 AM

hmm... I'm guessing that's not my problem then. The readings were 126 HC and 2.13 CO% @ 15mph, 117 HC and 1.82 CO% @ 25 mph.

Thanks for the info

BigBlocksRule · 10-13-2010, 07:52 AM

Sorry I can't help more, but we don't have emissions testing out here in dry, flat, treeless West Texas. The wind magically carries our pollution to never-never land and disappears it.

ChevyTech · 10-13-2010, 09:00 AM

There are two separate sensors.

One in the cylinder head, as BigBlocksRule stated, that is for the dash gauge, and another in the intake for the ECM.

The computer uses the coolant temp to determine how much fuel to inject and how fast the idle speed should be.

It is common for these sensors to fail.

To test the coolant sensor, unplug the wire connector and test the resistance across the two terminals of the SENSOR with an ohm meter.

If you see any coolant leaking out the terminals replace it.

If the terminals in the connector are corroded replace the “pigtail”.

The sensor screws into the intake manifold, on the front passenger side, by the thermostat housing.

Coolant sensor approximate resistance specifications:
177 ohms @ 212 deg. F. or 100 deg. C.
241 ohms @ 194 deg. F. or 90 deg. C.
332 ohms @ 176 deg. F. or 80 deg. C.
467 ohms @ 158 deg. F. or 70 deg. C.
667 ohms @ 140 deg. F. or 60 deg. C.
973 ohms @ 122 deg. F. or 50 deg. C.
1188 ohms @ 113 deg. F. or 45 deg. C.
1459 ohms @ 104 deg. F. or 40 deg. C.
1802 ohms @ 95 deg. F. or 35 deg. C.
2238 ohms @ 86 deg. F. or 30 deg. C.
2796 ohms @ 77 deg. F. or 25 deg. C.
3520 ohms @ 68 deg. F. or 20 deg. C.
4450 ohms @ 59 deg. F. or 15 deg. C.
5670 ohms @ 50 deg. F. or 10 deg. C.
7280 ohms @ 41 deg. F. or 5 deg. C.
9420 ohms @ 32 deg. F. or 0 deg. C.
12300 ohms @ 23 deg. F. or -5 deg. C.
16180 ohms @ 14 deg. F. or -10 deg. C.
21450 ohms @ 5 deg. F. or -15 deg. C.
28680 ohms @ -4 deg. F. or -20 deg. C.
52700 ohms @ -22 deg. F. or -30 deg. C.
100700 ohms @ -40 deg. F. or - 40 deg. C.

70c-10 · 10-13-2010, 12:24 PM

thanks chevytech.

ChevyTech · 10-13-2010, 10:45 PM

You’re welcome!

I will reply to your - stalling, erratic idle thread.

10-13-2010, 01:43 AM	#1
70c-10 Registered User Join Date: Oct 2005 Location: redlands, ca Posts: 112	failed smog - bad coolant temp sensor? Does a 1988 Chevy c1500 have two coolant temp sensors, or just one (ie - one for the computer and a separate one for the temp gauge)? My temp gauge seems to be working ok, but results from a failed smog test show that the engine is running rich. I have already replaced the o2 sensor. I am wondering if I should replace coolant temp sensor too. If the temp gauge and the computer use the same sensor, is it possible for it to work for the gauge, but not allow the engine to enter a closed loop? __________________ 6 in a row, makes it go!!! My Car '88 SWB Daily Driver Last edited by 70c-10; 10-13-2010 at 03:05 AM.

10-13-2010, 03:02 AM	#2
BigBlocksRule Registered User Join Date: Jun 2008 Location: Lubbock, TX Posts: 2,047	Re: coolant temp sensor Gauge sensor is in the driver's side cylinder head, intake coolant temp sensor is on the front of the intake. It could be going bad, but will definitely be noticeable if it's out - it'll run pig rich and rough, the engine will think that the coolant is -50* or so.

10-13-2010, 03:04 AM	#3
70c-10 Registered User Join Date: Oct 2005 Location: redlands, ca Posts: 112	Re: coolant temp sensor hmm... I'm guessing that's not my problem then. The readings were 126 HC and 2.13 CO% @ 15mph, 117 HC and 1.82 CO% @ 25 mph. Thanks for the info __________________ 6 in a row, makes it go!!! My Car '88 SWB Daily Driver Last edited by 70c-10; 10-13-2010 at 03:04 AM.

10-13-2010, 07:52 AM	#4
BigBlocksRule Registered User Join Date: Jun 2008 Location: Lubbock, TX Posts: 2,047	Re: coolant temp sensor Sorry I can't help more, but we don't have emissions testing out here in dry, flat, treeless West Texas. The wind magically carries our pollution to never-never land and disappears it.

10-13-2010, 09:00 AM	#5
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	Re: coolant temp sensor There are two separate sensors. One in the cylinder head, as BigBlocksRule stated, that is for the dash gauge, and another in the intake for the ECM. The computer uses the coolant temp to determine how much fuel to inject and how fast the idle speed should be. It is common for these sensors to fail. To test the coolant sensor, unplug the wire connector and test the resistance across the two terminals of the SENSOR with an ohm meter. If you see any coolant leaking out the terminals replace it. If the terminals in the connector are corroded replace the “pigtail”. The sensor screws into the intake manifold, on the front passenger side, by the thermostat housing. Coolant sensor approximate resistance specifications: 177 ohms @ 212 deg. F. or 100 deg. C. 241 ohms @ 194 deg. F. or 90 deg. C. 332 ohms @ 176 deg. F. or 80 deg. C. 467 ohms @ 158 deg. F. or 70 deg. C. 667 ohms @ 140 deg. F. or 60 deg. C. 973 ohms @ 122 deg. F. or 50 deg. C. 1188 ohms @ 113 deg. F. or 45 deg. C. 1459 ohms @ 104 deg. F. or 40 deg. C. 1802 ohms @ 95 deg. F. or 35 deg. C. 2238 ohms @ 86 deg. F. or 30 deg. C. 2796 ohms @ 77 deg. F. or 25 deg. C. 3520 ohms @ 68 deg. F. or 20 deg. C. 4450 ohms @ 59 deg. F. or 15 deg. C. 5670 ohms @ 50 deg. F. or 10 deg. C. 7280 ohms @ 41 deg. F. or 5 deg. C. 9420 ohms @ 32 deg. F. or 0 deg. C. 12300 ohms @ 23 deg. F. or -5 deg. C. 16180 ohms @ 14 deg. F. or -10 deg. C. 21450 ohms @ 5 deg. F. or -15 deg. C. 28680 ohms @ -4 deg. F. or -20 deg. C. 52700 ohms @ -22 deg. F. or -30 deg. C. 100700 ohms @ -40 deg. F. or - 40 deg. C. __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too.

10-13-2010, 12:24 PM	#6
70c-10 Registered User Join Date: Oct 2005 Location: redlands, ca Posts: 112	Re: coolant temp sensor thanks chevytech. __________________ 6 in a row, makes it go!!! My Car '88 SWB Daily Driver

10-13-2010, 10:45 PM	#7
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	Re: coolant temp sensor You’re welcome! I will reply to your - stalling, erratic idle thread. __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too.



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