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UHF
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engine not getting hot enough -Chevy Blazer

2000 Chevy Blazer 4x4 4.3L engine

Engine running cold, not heat in cab. Assumed t-stat had failed. Replaced it. Same thing, engine gets to maybe 135° F, and poor heat in cab. I noticed the fan runs as soon as the truck is started, even with a temperature of 33°F and a cold engine that's been sitting all day. I assumed the fan clutch was bad and just finished replacing it.

The symptoms remain the same. Engine running about 135° and no/poor heat in cab. Upper radiator hose was cool to the touch after a 15 mile trip on the highway with outside temps at 23°.

What now?? I'm not very savy when it comes to automotive repair, but I just can't afford to take this thing to the shop right now.


MikeTest
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join:2010-10-19
Moribund


Clogged heater core is the prime suspect. Someone else will have to chime in whether it's worth trying to flush or how much it should cost to replace.


UHF
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reply to UHF
Clogged heater cores are common on this vehicle, but why would that make the engine itself run cold?

It's over $900 to replace the core, according to my neighbor who did have a clogged core.


MikeTest
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join:2010-10-19
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1 recommendation

said by UHF:

Clogged heater cores are common on this vehicle, but why would that make the engine itself run cold?

It's over $900 to replace the core, according to my neighbor who did have a clogged core.

IDK,

Did you bleed the air out of the cooling system after swapping the T-Stat?

»www.scribd.com/doc/12986652/1997 ··· r-Manual gives a decent description how to do it, minus the patch pills.

Maybe you'll get lucky and it's just air-bound.

59181437

join:2011-02-01
reply to UHF
You try the old way of making it run hotter, place a piece of cardboard in front of the radiator.


Cho Baka
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reply to UHF
A clogged heater core should not make the engine run cold.
Air in the system should also not make the engine run cold, although it may result in lack of heat and fluctuating or too hot temperature readings (if not overheating).

A poor quality thermostat will make the engine run cold.
Where did you buy it, what brand was it, and what temperature was it?

My first guess would still be a bad or incorrect thermostat.
--
The talented hawk speaks French.


UHF
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said by Cho Baka:

A poor quality thermostat will make the engine run cold.
Where did you buy it, what brand was it, and what temperature was it?

My first guess would still be a bad or incorrect thermostat.

It's a NAPA Premium 195 degree stat. The previous one didn't appear to be stuck, but I replaced it anyway since I was in there.

After bleeding the air as MikeTest suggested, I'm getting heat (100-120 at the vents). The temp gauge is still reading low, but checking the coolant line right at the thermostat with an infrared thermometer shows the temp is just above 180. I should mention that when I said the radiator hoses were cold, that was after changing the stat but before changing the fan clutch. I think the fan was the problem, but I also introduced some air into the system when replacing the t-stat.

I'm going to drive it for a couple more days and see how it acts, but at this point it appears to be working.

Thanks for the tips, guys!


hortnut
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reply to UHF
What ratio of water to coolant did you install?

Wrong ratio can cause problems. I am not an expert, just recall reading something on this recently.

»www2.gi.alaska.edu/ScienceForum/ ··· 680.html

»www.marinemechanic.com/site/page ··· e39.html

Hopefully some of the Auto folks will chime in.


The Pig
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1 edit
reply to UHF
Is the floor of your cab wet? Bad news core has a leak and will have to be replaced, I got 2 prices on my sons car one for $835 and another for $740.
You (yourself) can do a reverse flush of the heater core that may solve the problem.
Open you radator cap to release the water pressure, then find where the 2 hoses go into the firewall (going into the dashboard) and carefully remove them (don't twist them if you can avoid it) and put a garden hose with sprayer on it in the out nipple (which on most autos is the one on the left when looking at them from the front of the vehicle) and let it rip then go the other way until the water is clear, replace hoses then fill the radiator with antifreeze (no 50/50 junk) and drive around for 20 minutes with the heat all the way up to make sure the anti-freeze mixed well with the water in the core!

fixrman
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reply to UHF
The only thing that would make the engine run cold would be if the thermostat was stuck wide open.

A clogged core would exhibit low or no heat but the vehicle operating temperature would be normal. An air pocket is the most likely scenario. By the way, what came out of the system when you drained it? That is a major clue into what is going on with the system. If brown sludge was noted, whether in the coolant, overflow bottle or gathered around the neck of the radiator fill on the inside and inside the cap, then you have iron oxide sludge circulating in the cooling system. Any Dexcool® - filled system can exhibit this.

Incidentally, flushing an 11 year old heater core is inviting disaster. If the core is clogged, it needs to be replaced and the entire cooling system needs to be cleaned and flushed. Do want you want there, but Smart Money says that putting Dexcool® back into that system is only a re-invitation to the same scenario.
--
"from a broken heart to a hole in the sky"


Wholigan

join:2001-03-28
Buffalo, NY
reply to Cho Baka
3SGTE is correct yet it is possible you put the new thermostat in backwards? Very easy to make this mistake. I would also suggest disconnecting both heater hoses and flushing the heater core with a garden hose. As someone said earlier its a frequent issue on these trucks.


Cho Baka
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reply to Cho Baka
I should add, if it is very cold outside, then it could just be that it is too cold.

I had a few cars that with certain ambient temperatures (less than -30) would not reach operating temperature when the heater was set to high and the vehicle was idling or being driven at low speeds/loads.
--
The talented hawk speaks French.


The Pig
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reply to fixrman
said by fixrman:

Incidentally, flushing an 11 year old heater core is inviting disaster. If the core is clogged, it needs to be replaced and the entire cooling system needs to be cleaned and flushed. Do want you want there, but Smart Money says that putting Dexcool® back into that system is only a re-invitation to the same scenario.

If the core is clogged what harm can there be in trying a flush?
It's screwed anyways! And if the flush works then the OP just saved over $700!


Gemstone
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reply to UHF
One of my cars is a 2001 Impala LS with a 3.8L engine. A few years ago I had the same type of problem. Engine running cold all the time. Thought it was a bad t'stat so I changed it out. Same problem. Then I noticed the radiator cooling fans were running all the time. So I plugged in my DTC reader and got a code for the ECT sensor (Engine Coolant Temp Sensor). I change the ECT sensor and cleared the code and the problem remained. A friend told me the code had to get cleared "twice" before things would go back to normal. So I cleared the ETC problem code again and then all was normal. Fans turn on and off at the proper temps. Been good for over 2 years now.
--
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UHF
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reply to hortnut
said by hortnut:

What ratio of water to coolant did you install?

50/50 Dexcool.


UHF
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reply to The Pig
said by The Pig:

Is the floor of your cab wet?

Nope. It's not leaking! Been there, done that with a car I had in high school.


UHF
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2 edits
reply to fixrman
said by fixrman:

By the way, what came out of the system when you drained it?

I didn't drain it. I just pulled the stat and let what little coolant came out leak onto the floor. There is some sludge around the filler neck, but very little. The system was flushed a year ago and refilled with Dexcool at a dealership. I asked for the green stuff, and they told me I had to use Dexcool. I may flush all that crap out and replace it with regular antifreeze, but I prefer to wait until spring time when I can get to the garden hoses and not have to deal with the cold weather while doing it.


UHF
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reply to Gemstone
said by Gemstone:

Then I noticed the radiator cooling fans were running all the time. So I plugged in my DTC reader and got a code for the ECT sensor (Engine Coolant Temp Sensor). I change the ECT sensor and cleared the code and the problem remained. A friend told me the code had to get cleared "twice" before things would go back to normal. So I cleared the ETC problem code again and then all was normal. Fans turn on and off at the proper temps. Been good for over 2 years now.

It's a thermostatic fan clutch, nothing electrical, so a sensor can't be making it run all the time. But that was my first thought after changing the t-stat as well.

I'll post an update tomorrow after I drive to work in the morning, that will give me a good 15 miles of highway driving, and I have a good Fluke infrared thermometer at work so I can get an actual engine temp right at the stat, along with ambient air temp and the heat vent temps. I'm keeping my fingers crossed that everything will be fine!

Thanks again for all the posts, I'm really hoping to learn as much as I can about this stuff, I'm tired of paying big bucks for things I can fix myself.


UHF
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reply to UHF
I bit more info after today's drive to work. Vehicle ran for a good 40 minutes, 20 of which was at highway speeds. Air was blowing lukewarm, about 80 degrees when I arrived at work. After running for 20 more minutes it was blowing at 115 degrees measured with a thermocouple on a Fluke 179.

All measured with the thermocouple:
Outside air temp 20F
Radiator Upper hose 110
Radiator Lower hose 110
Tstat temp measured 170 with the thermocouple, 196 with a Fluke 62 infrared thermometer
Core1 hose 132
Core2 hose 125

All temps measured quite a bit warmer with the infrared. Not sure which to believe, but the upper radiator hose felt a lot hotter than 110.

The engine temp guage reads 160-170, but hard to say, the only numbers they give are at 100, 210, and 260. Needle used to stay just a hair below 210 up until a week or two ago.

I guess the next step should be to pull the thermostat and test it in hot water to see what temp it opens at?

Or maybe a better idea is tell my wife how much I'd love to switch trucks with her since I know she likes my heated seats, LOL.


mattmag
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I really have to believe that your replacement thermostat is faulty. I know it seems illogical, but I've had it happen plenty of times so it isn't unheard of. I would get a replacement stat, as that one should be covered under warranty by NAPA. Just tell them it opens too early, and get another one. There really isn't anything else that would cause the problem of *under* heating.

You are right that in most cases the dash temperature gauge will read about 210 when everything is normal.

It is difficult to get proper temp reading with an IR tester on rubber hoses by the way, so don't be frustrated with that. You always want to try and check metal pieces, like the thermostat housing.


UHF
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said by mattmag:

It is difficult to get proper temp reading with an IR tester on rubber hoses by the way, so don't be frustrated with that. You always want to try and check metal pieces, like the thermostat housing.

I've noticed anything too shiny, and anything that is dull black is hard to measure with the IR. It certainly seems to me to be a thermostat issue. I can't think of anything else it could possibly be.

HarryH3
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reply to UHF
Did you install the rubber o-ring style gasket on the thermostat, as seen here: »www.autozone.com/autozone/parts/ ··· 1_11542_

If you just used the older style fiber gasket then a small trickle of coolant can leak past the stat. It doesn't take much in really cold weather to keep the engine too cool.


cdru
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reply to UHF
I previously had a Montana minivan that during the winter on very cold days, the upper heater hose wouldn't get much past warm even after the engine was driven for a long time. Just about any movement faster then stopped generated enough air flow to cool the engine enough that the thermostat never fully opened.

Find out what the temperature rating for the thermostat is. It's probably somewhere around 195-210. Drop it in a pot of water and watch what it does. If it opens significantly before boiling, then you have a defective thermostat.


Gemstone
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reply to UHF
Here are a couple of possibly useful or useless comments from me:

1.) Measurements using an IR "camera" or "thermometer" can be very inaccurate unless the emissivity of the surface you are measuring is known and set properly into your instrument. Some IR tools are preset with an emissivity of 0.9 and others are settable.

2.) I once bought a thermostat called a "failsafe" thermostat. The trick with it was that if it fails it has a spring clip that locks it open. Therefore you engine cannot overheat due to a stuck closed t'stat. The problem was, it was defective right out of the box, and stuck open within the first day of use. Took me a few days to figure out my brand new t'stat was defective. I then went back to a conventional OEM t'stat.
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fixrman
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reply to The Pig
It is an exercise in futility. If the core is 11 years old and is clogged, after the flush it will leak. Would you like to see the scrap pile?

Have you ever seen the cross section of a heater core? The passages are smaller than in a radiator, so all a flush accomplishes is a delay of the inevitable - if it works at all. We have been requested to flush five this winter; three out of the five leaked, one could not be flushed and one worked for two weeks before clogging again.
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UHF
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reply to UHF
No rubber o-ring, but the t-stat has a rubber gasket with it.

It's a 195 degree stat. I tested the one I removed, it didn't open with the water temp at 195, so it looks like the t-stat was never the problem.

Wouldn't I see a significant difference in temperatures between the inlet and outlet lines if the heater core were clogged? Or maybe not since very little coolant would be flowing. At this point I've given up and it's going to the shop in the morning. I really hope I don't need the heater core replaced, I'm already thinking of what I can sell on ebay if I have to pay for that sort of repair bill

fixrman
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A thermostat calibrated to 195 degrees starts to open at 195° , but isn't fully open until about 203° .

How is the flow in the vehicle? You might have an issue with the water pump impeller.
--
"from a broken heart to a hole in the sky"


santy
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If the water pump impeller isn't pushing/flowing the coolant properly, the vehicle will run hotter not colder.

I had a vehicle at one time that would overheat. Tried t-stat, coolant flush etc. finally took off the water pump and the impeller was slipping on the shaft. The drag of trying to move the coolant was enough to keep the impeller from turning even tho the fan/pulley was spinning fine and it didn't make any noise.
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Sly
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reply to UHF
If this is a fail safe thermostat, remove it. They are designed to open up fully (and permanently) if the engine ever over heats. The problem is, they are cheaply made and will often open even if your engine has never overheated. If that happens, your engine will do exactly what you are describing. It will never fully heat and will get cooler the faster you drive.

I had the same thing happen on my F150. The engine would never fully heat up and so I replaced that stat, fan clutch and temperature sensors (only when one of them didn't fix the problem). It still wouldn't heat up and so I finally pulled the stat out again and this time put in a regular thermostat. Problem solved.
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The Pig
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reply to UHF
When the hell did thermostats become so expensive?