Jump to content

Not heating up? 1996 GMC 1500


Recommended Posts

So I just bought a 1996 GMC 1500 for work and I can't get it to heat all the way up. It's almost at 195 but falls short and I'm not sure if I'm over reacting and should leave it or fix it. It has a new radiator, New 195 thermostat, the coolent sensor is new and the coolent sender is new, and I tested the gauge itself and that works fine. Heater core hoses are both hot. Anything I'm missing?! Thanks for the help! I'm in Minnesota so just want to make sure everything's working before winter.

post-165670-0-91071800-1504057828_thumb.jpg

post-165670-0-91071800-1504057828_thumb.jpg

post-165670-0-91071800-1504057828_thumb.jpg

post-165670-0-91071800-1504057828_thumb.jpg

Link to comment
Share on other sites

Maybe your gauge isn't super accurate...... Each mark is worth 14 degrees almost.

 

What was it like prior to all the changes?

 

Personally. I'd have no worries

 

 

Edit to add.... You could take a non-contact thermometer and take readings to compare to dash gauge

Link to comment
Share on other sites

you mean heat in the cabin?

 

as that is where my gauge is going up a hill with a/c on and a boat in tow in the summer.

 

if concerned for engine, the computer starts full warm chores at 160 ish.(I monitored live data via obd2 scanner - I was bored)

 

the heaters in these, especially the pickups. holy cow. Most powerful I have ever run. I even turn it down below zero in a maines version of a dark winter day.

 

they do make noises to change functions, just listen in on the cold to warm, or hit the outside/recycle air button.

 

..and the other thing is the sleeve bearing heater motors. Truly terrible in long runtimes. ebay has ball bearing versions for all years.

Link to comment
Share on other sites

If the upper radiator hose gets hot, then the thermostat is opening.

 

You could check the coolant temperature sensor reading with a scanner, but I think you're fine.

 

For comparison, both of my 98 models show the same gauge reading. I don't remember which thermostats I have, but think they're 195 or so.

 

I think the temp gauge is more for decoration than anything else. The markings don't really make a lot of sense.

 

6c75a567858b3bfedced897d00a5ed75.jpg

 

 

Sent from my iPhone using Tapatalk

Link to comment
Share on other sites

I had a similar problem with my '94 4.3L. After trying several senders and getting poor results, I measured it with a non-contact thermometer at the thermostat housing, checking the resistance of the sender, and comparing that to a table. The resistances were different from the table and, in fact, the resistance curve was different - it's not a linear response.

 

I suspect the parts manufacturers are just substituting a part with the same threads and wiring connection to fit a broader range of engines so they don't have to continue building as many parts for trucks that are becoming more and more rare as they age. I could no longer get the actual GM part. I suspect they are just looking at the external connections when they say it is OEM compatible.

 

In my situation I'm more concerned with overheating so I removed the gauges and moved the needle on the gauge so it is more accurate when hot. It sits on the first mark to the left of the 210 mark when warmed up. That should be ~195 and I have a 195 thermostat. But it sits between the first and second mark to the right of the 100 degree mark on the left side when it's cold which would be ~125. That's obviously wrong when it's 90F outside but I'm not worried about the low end reading. I don't care what it reads when I first start it but I'll know I have an issue when it passes the 210 mark while driving down the road.

Link to comment
Share on other sites

Couple of things, does your OBD scanner read the same temp as the ambient air when the truck is cold? Should be within 1 to 2 degrees. Resistance at 70 degrees ambient should be around 3400 ohms for the ECT sensor.

 

Does you truck get to full warm up (195 degrees) within 7 minutes from start up sitting in the drive way with heater / AC off ?

 

If you have access to a stick type temp gauge place temp gauge in the center vent a few inches, turn the blower motor to the lower 2 settings. When truck is at 195 degrees according to the scan tool, vent temp should be 150 degrees or so, more the better.

 

If you put in an aftermarket temp sending unit, or have the very old original, the resistance values are not the same as a new factory unit. Coolant sensors do lose calibration.

 

If you test your coolant sensor, the ohm value at 195 degrees should be around 236 to 260 ohms.

 

Find a lower 200 something ohm resistor or a variable 1k range potentiometer (solder only two wires where you get a variable resistance signal) from an electronic repair shop / Radio Shack / electronic parts supplier. Stick one end of the resistor in the coolant sensor connector, the other to ground. Same procedure for the potentiometer. Temp gauge should be around 210 degrees. Potentiometer will adjust the temp gauge if under 1K ohms. If this works, replace the coolant sensor, get one from Delco or the dealer, ...not aftermarket because of different resistance values / quality control.

 

Here is an ohm chart for engine coolant sensors, not computer coolant sensors for the early 90's GM vehicles.

 

 

Here’s a temp/resistance/voltage chart for a typical GM sensor early ’90s

 

Coolant Temp Resistance Voltage

-40℉ 100,000 Ω 5.00V
+33℉ 9,600 Ω 4.50
+57℉ 4,095 Ω 4.00
+78℉ 2,975 Ω 3.50
+100℉ 1,800 Ω 3.00
+120℉ 1,350 Ω 2.50
+143℉ 835 Ω 2.00
+163℉ 432 Ω 1.50
+186℉ 305Ω 1.00
+210℉ 185Ω 0.75
+234℉ 60Ω 0.50

 

Hope this helps???

Link to comment
Share on other sites

95 Tahoe Sport - yep. That's about as hot as I've seen it. I like all my gauges in the middle - makes me feel like everything is normal. But the temp never gets there. I guess it's better than past the middle.

Link to comment
Share on other sites

The resistance sent back to the temp gauge is very important. Like I said earlier, temp gauge senders do wear out. Cheap senders are not that accurate. Gotta measure the resistance at the sending unit cold, then warm. Follow my instructions and get your needles to where they belong.

Link to comment
Share on other sites

  • 2 weeks later...

If the upper radiator hose gets hot, then the thermostat is opening.

 

You could check the coolant temperature sensor reading with a scanner, but I think you're fine.

 

For comparison, both of my 98 models show the same gauge reading. I don't remember which thermostats I have, but think they're 195 or so.

 

I think the temp gauge is more for decoration than anything else. The markings don't really make a lot of sense.

 

6c75a567858b3bfedced897d00a5ed75.jpg

 

 

Sent from my iPhone using Tapatalk

I would be more worried about that alternator than the temp sensor! lol

Link to comment
Share on other sites

When the motor is cold measure the resistance of the coolant sensor, then measure the resistance with the coolant sensor again when the engine is fully warmed.

 

Also, GM defines an overheat when the motor temp get's to 235F.

 

I will leave you a GM temp chart to tell you where you sensor resistance should be.

 

Most people will disagree with me, but get a "Delco" coolant temp sending unit since it has the "factory calibration" of resistance where the aftermarkets might be off a little.

 

 

post-175614-0-68901300-1506042132_thumb.jpg

 

 

 

 

 

 

.

post-175614-0-68901300-1506042132_thumb.jpg

post-175614-0-68901300-1506042132_thumb.jpg

post-175614-0-68901300-1506042132_thumb.jpg

Link to comment
Share on other sites

I would be more worried about that alternator than the temp sensor! lol

Lol, yeah it doesn't look too good according to the dash gauge but shows around 14V out at the battery when running. Guess the cluster is the issue.

 

Thanks for pointing it out, though.

 

 

Sent from my iPhone using Tapatalk

Link to comment
Share on other sites

east321

 

In your above picture, the volt gauge indication is a very heavy load condition, which in turn is either a no /or low alternator amp output condition for the rpm's that were running when the picture was taken. It is not any volt gauge malfunction.

Link to comment
Share on other sites

east321

 

In your above picture, the volt gauge indication is a very heavy load condition, which in turn is either a no /or low alternator amp output condition for the rpm's that were running when the picture was taken. It is not any volt gauge malfunction.

You know, I think you may have saved me from a breakdown.

 

I was driving it this morning and noticed the gauge dipping. Checked it again, alternator output was 13.2V at idle. Turned on all of the accessories and it was at 9V.

 

Replaced the alternator, here are the voltage readings between the alternator post and battery negative:

 

Accessories on, idle: 12.98V

Accessories off, idle: 14.33V

 

Accessories on, 2000-rpm: 14.23V

Accessories off, 2000-rpm: 14.36V

 

Battery voltage 30-minutes after above tests: 12.55V

 

This is what the gauge shows for 12.98V between alternator post and battery ground.

 

33d720bd63a38d5a939ffe66e79968b8.jpg

 

This is the gauge at 14.33V...

 

ec149f1ed1999d9d0c94c1e64c68a684.jpg

 

I replaced the battery cables when I did the starter last week.

 

What do you think?

 

 

Sent from my iPhone using Tapatalk

Link to comment
Share on other sites

I hope you bought the highest amperage alternator that fits on your motor.

 

I find too many people are too cheap to buy the right size amperage and continue to have voltage output problems for eon's.

 

Rule of thumb when buying any alternator, .....you buy the highest amperage the car can take. It avoids a lot of electrical headaches.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.



×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.