1980 C10 temp light remaining on. VERY frustrating!!! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

kaysboat · 10-19-2018, 10:24 AM

Hello,

I have a 1980 Chevy C10 with the 250 Straight six and temp light (as opposed to the gauge).

The temperature warning light is staying on even from initial start up and I don’t know what the issue is. So far I have:

1. Ensured coolent was topped up;
2. Flushed coolent;
3. Checked that coolent was circulating (rad temp fine, hoses warm, heat from heater etc...)
4. Changed thermostat;
5. Changed temp sending unit (heat sensor);
6. Ensured fuse was 20 amp and not blown; and
7. Took it to a shop. They checked the temperature of the coolent (runs about 190 degrees) and did a sniff and chemical test of coolent to ensure head gasket not cracked. It’s not.

At this point I’m stumped, and although I’m pretty confident in driving it without it actually overheating, I hate driving with warning lights on. Any help/ideas would be great.

Thanks.

**hatzie** · 10-19-2018, 11:38 AM

Does it get brighter as she warms up?

kaysboat · 10-19-2018, 11:52 AM

No it stays pretty much the same

Dead Parrot · 10-19-2018, 01:11 PM

IIRC, that sensor is a 'Gets too hot, closes circuit to ground' setup. Check for a short in the sender line. Melting to the exhaust manifold or cut on a sharp edge.

Does the light go out if you pull the wire off the sender? If so, possible that both the old one and new one are bad.

**hatzie** · 10-19-2018, 05:28 PM

Quote:

Originally Posted by Dead Parrot

IIRC, that sensor is a 'Gets too hot, closes circuit to ground' setup. Check for a short in the sender line. Melting to the exhaust manifold or cut on a sharp edge.

Does the light go out if you pull the wire off the sender? If so, possible that both the old one and new one are bad.

I was wondering if someone slipped a temp gauge sender in the lamp switch hole...

If it goes out when you unplug the switch the switch is bad or the wrong one. I agree about checking for the wire melted to the exhaust manifold... that's a common failure point.
The warning lamp switches are cheap. Standard Motor Products TS135 is the nailhead warning lamp switch for the 1980 C10 with a 250 I6. It looks similar to the 01513321 nailhead temp sender for 60's & 70's GM gauges.

Pontiac1976 · 10-21-2018, 05:32 PM

Quote:

Originally Posted by Dead Parrot

IIRC, that sensor is a 'Gets too hot, closes circuit to ground' setup. Check for a short in the sender line. Melting to the exhaust manifold or cut on a sharp edge.

Does the light go out if you pull the wire off the sender? If so, possible that both the old one and new one are bad.

I have to agree with this post.

10-19-2018, 10:24 AM	#1
kaysboat Registered User Join Date: Jul 2013 Location: Nova Scotia Posts: 27	1980 C10 temp light remaining on. VERY frustrating!!! Hello, I have a 1980 Chevy C10 with the 250 Straight six and temp light (as opposed to the gauge). The temperature warning light is staying on even from initial start up and I don’t know what the issue is. So far I have: 1. Ensured coolent was topped up; 2. Flushed coolent; 3. Checked that coolent was circulating (rad temp fine, hoses warm, heat from heater etc...) 4. Changed thermostat; 5. Changed temp sending unit (heat sensor); 6. Ensured fuse was 20 amp and not blown; and 7. Took it to a shop. They checked the temperature of the coolent (runs about 190 degrees) and did a sniff and chemical test of coolent to ensure head gasket not cracked. It’s not. At this point I’m stumped, and although I’m pretty confident in driving it without it actually overheating, I hate driving with warning lights on. Any help/ideas would be great. Thanks.

10-19-2018, 11:38 AM	#2
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,913	Re: 1980 C10 temp light remaining on. VERY frustrating!!! Does it get brighter as she warms up? __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

10-19-2018, 11:52 AM	#3
kaysboat Registered User Join Date: Jul 2013 Location: Nova Scotia Posts: 27	Re: 1980 C10 temp light remaining on. VERY frustrating!!! No it stays pretty much the same

10-19-2018, 01:11 PM	#4
Dead Parrot Registered User Join Date: Aug 2012 Location: Oklahoma City, OK Posts: 2,477	Re: 1980 C10 temp light remaining on. VERY frustrating!!! IIRC, that sensor is a 'Gets too hot, closes circuit to ground' setup. Check for a short in the sender line. Melting to the exhaust manifold or cut on a sharp edge. Does the light go out if you pull the wire off the sender? If so, possible that both the old one and new one are bad.



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