over cooling

faller49 · July 8, 2019

1992 c1500, 2 wheel drive ,auto ,5.7

no recent work other than new battery a week ago and problem started long before that

engine over cools.. just started about 6 months ago.. I replaced the t-stat with a NAPA one and engine will get warmer but then drops right back to low temp

tried one from CARQUEST and same result.. Low is approx. 150F maybe 160 F.. (estimating on gauge.) Tstats are all 195 F and it will peak at about where that should be and where it has always ran before but then drops back to the low area again.. It will fluctuate very slightly ..maybe 15 degrees but always go to lowest .. About the only time it goes to 'normal ie195' is on initial start and warm up which it would not do with orginal tstat (since occurrence of the problem) so new ones did provide some change.

Thoughts.

Thanks..

TW97C1500 · July 9, 2019

You may want to see if you can get a "loan-a-tool" infrared thermometer from a parts store and measure the actual temperature, say right on the thermostat housing. It could simply be that the temperature sensor (temperature sending unit / "thermometer") is messing up. I'm sure there is somebody who knows what the electrical reading should be (voltage I assume, maybe resistance). You could take it out and put it in boiling water, which you know will be about 212 (depending on altitude), so it should have a certain reading at that temp. Or just replace it and see if that helps. The ol' parts cannon method.

faller49 · July 9, 2019

_{Thank You for your reply.. dummy me.. I happen to own a infrared thermometer and did not think about using it.. (old is hard LOL ).. the add to confusion part is that the gauge has more fluctuation after the T-stae changes then it did previous. and why does it go all the way to the '195' mark on first run then fall back and fluctuate between 150 ish and 175 ish…. but never goes back to the '195 area again..}

_{JUST ASKING.. could it be my fan clutch and how would I tell..}

_{Power does not seem affected but gas mileage sure is..}

riverbanks · July 9, 2019

Gas mileage suffering?,cluth fan or coolant temperature sensor,first, clutch fan staying engaged when not needed,2,c.t.s staying low,rich condition,is the tailpipe,black as coal?

faller49 · July 9, 2019

ok.. I have something weird going on here.

first some past information.. I own 3 rigs.. my wife drives 5 miles to work.. in the winter .. high 30 to high 40 temps.. my wife for the last few years has preferred to drive this pickup to work because it gets warm the fastest.... (in this problem time the heater puts out warm air but not the usual hot air)

So to day I drove to her work.. 75 degrees out.. and it just barely started to get warm when I got to her work place.. I parked and got the laser out and did some looking.

hose at thermostat housing .. 124 degrees .. lower hose 87 degrees .. radiator cap 82 degrees..

SO.. I set there and let it ideal for 20 minutes.

Hose at T-stat housing 155.. lower hose 123... cap.. 99.

Gauge at about mid gauge point or what I approx. at 150 to 160... (After the idle time)

Took it for a 20 mile highway drive.. Gauge stayed mostly steady with occasional slight fluctuations up then down to same spot.. Never up to 195 area where it has ran for years...

stopped at the market after the 20 mile drive and was checking it again with the laser when a guy comes up and asks if I needed help.. I told him I was starting to not trust my laser thermometer.. Low and behold.. he has one and starts pointing to same places I was.. they were both the same within 1 or 2 degrees so that helped my mental state..

The numbers we both got were within 3 to 5 degrees of what is stated previous..

I did my shopping.. got gas and drove the 5 miles home.. on the way home the gauge started holding higher (hotter) and maintained it.. I turned on the heater and it was very much warmer than has been...when I got home I jumped out and did more checking..

Hose at T-state housing 186... lower hose 146... cap 141.. Not as high as they should be but gauge was running higher than it has for weeks and these temps were higher than any other testing..

I shut the truck off and grabbed the fan and it will spin..

My brain is muddled at this point.. I do not claim to be a mechanic but I do manage to keep a 1997 Taurus.. a 2000 Caravan ...and this truck running for several years and none of them have ever been in a shop since I have owned them..

I do appreciate the help and thoughts..

And.. the exhaust is black.. with a running rich type of loose soot coating.

riverbanks · July 9, 2019

I would get a new coolant temperature sensor,this one is for the e.c.m.,not guage, it is running rich,and rich is cooler temp,only other item to check is spray pattern on injectors,a nice cone shape is ideal

TW97C1500 · July 9, 2019

You might have 2 things going on, maybe the temperature sensor, and possibly air trapped in the system. Trapped air would explain the quirky behavior and the fact that it is getting back to normal temperatures. Every time you start it and get it up to temperature, then let it cool down, it will self-bleed some air out, IF you don't have a leak and you're overflow tank is still there. That's the "official" method to bleed it, temperature cycle 5 or 6 or 8 times.

riverbanks · July 9, 2019

Your post brings up more possibilities,trapped air,yikes,cracked head or blown head gasket

faller49 · July 9, 2019

While I do plan on changing both sensors and finding a quality T-stat and changing it ..yet again.. However, I do not think the sensors are the problem as they would have no effect on my laser readings..

I also was thinking more than one thing going on.. AND old brain might have bit me again..

The mention of air in system reminded me of a step I forgot to mention.. While checking at the market and the other fella had whipped out his infrared thermometer he commented that the cap was cool to the touch to him and I agreed and I partially opened it until hot water started coming out and I tightened it back up.. It after that that I gassed up and drove home and the temps came up.. Not up to what they should be but a lot closer than they had been.. I did drain the system.. or partially drain it when I changed the thermostat(s)… maybe part of current problems was that it had not purged?... Maybe these cheap thermostats are not accurate temp wise....

You guys are tops.. Thanks for all thoughts.. keep them coming..

riverbanks · July 9, 2019

Have faith in thermostats,all very close,but I only install ones with the bleeder hole,or I drill one in it,makes life a lot easier

TW97C1500 · July 10, 2019

Yeah, I've had it happen, as goofy as it sounds, where air in the system keeps the temp down. Maybe the air gets trapped at the thermostat and becomes a steam pocket, which is hotter, and that keeps the t'stat open although the liquid is cooler than it is supposed to be. My Grand Cherokee had a leak at the top seam of a brand new radiator, under the shroud where you could never see a drip, and it would run too cold on the highway but in traffic would get up higher than normal, not "too hot" but getting there. It was a 40+degree difference. I noticed the leak one humid day, changed the radiator (warranty), didn't do anything in particular to burp the air, simply drove it a couple of times to heat cycle, and it has pegged right at 195 for several years now, except on real hot days in traffic.

On the opposite hand, I had a 76 Jeep Wagoneer with a leak and if I filled it all the way up to the top, it would get hot on a long drive but you could loosen the cap and let is spew a little bit and it would run right on 180 for however many days until it had leaked too much out.