DupermanDave

My temp gauge used to sit just a little under the halfway mark on the meter. Suddenly, as of yesterday, its only been about 1/4 (one quarter) of the way "full". I have checked for leaks and found none. Checked all the hoses and they were all pretty hot, even the lower radiator hose. When the radiator cap is removed, I can hear the normal gurgle noise, so it is holding pressure.

Today and yesterday have been a little cooler than usual, but I've never seen the temperature go so low, even when pushing the truck hard and it's fully warmd up.

What should I be checking into at this point? Or is this normal and I need not worry?

4Crawler

iTrader: (3)

Might check your thermostat. Maybe it has stuck open.

DupermanDave

I thought about that. For about as much work that's required for checking the T-stat, I think I would just replace mine. I'd need to drive to my parent's, drain the coolant, remove the t-stat and replace it anyway if it tested to be bad. If it was bad, I'd need a lift to the dealer to order one anyway, so I may just head to the dealer and pick one up later on tuesday.

But until then, is there anything else I should look into? Will this hurt or damage anything if it is stuck open?

abecedarian

I think it's the thermostat. Even if the fan clutch were to seize and keep the fan spinning at engine RPM 100% of the time, the thermostat would still regulate the engine / coolant temp to your 'normal' reading. But do check your coolant level and burp the system if it's low.

The 91 did that several years ago, when it was my mother's. One day she complained to me that her heater hadn't been working well for a few months- basically luke-warm air. Pulled the thermostat and sure enough it was open, and it was about 60F outside and the engine was cold. Put a 195 in it and she was toasty within one mile and she started getting about 50 more miles out of a tank of gas.

DupermanDave

I tried to burp the system and see if the coolant would flow when the engine was cold. I removed the radiator cap and started the engine. After about 30 seconds the cooland level started to rise and it almost overflowed. Had something like this happen when I was burping the system a few months ago. Previously, the air bubbles kept coming out and would never stop. It was like a baking soda volcano.

Also, when going for a ride afterward, I turned on the (cold) air (no A/C) with the defoggers and noticed a really strong coolant smell. The fiance' says it was a musty smell with no sweetness to it, but I say it smelled like coolant.

Still sound like the t-stat? How much does one run from the dealer? Why pick dealer versus another OEM brand? (i see them for $12 on parts stores online)

DupermanDave

I tried to burp the system and see if the coolant would flow when the engine was cold. I removed the radiator cap and started the engine. After about 30 seconds the cooland level started to rise and it almost overflowed. Had something like this happen when I was burping the system a few months ago. Previously, the air bubbles kept coming out and would never stop. It was like a baking soda volcano.

Also, when going for a ride afterward, I turned on the (cold) air (no A/C) with the defoggers and noticed a really strong coolant smell. The fiance' says it was a musty smell with no sweetness to it, but I say it smelled like coolant.

Still sound like the t-stat? How much does one run from the dealer? Why pick dealer versus another OEM brand? (i see them for $12 on parts stores online)

Jay351

The dealer thermostat is a dual valve. IT prevents the famous 22re tempurature gauge overshoot at startup.

PT# 90915-03076 or 03070.. I can't read my messy writing

you sure your heater core isnt leaking or your hg?

iamsuperbleeder

yeah coolant smell in the cab is a sure sign of heater-core leaking

mine sprung a leak, and even with the AC on, there was a mist of hot coolant coming outta the vents... I had to bypass it cause it was making me nautious while driving the truck, and even started to hurt my chest from breathing it in... never did noticeably leak in the cab though, just from the vents... that was strange...

DupermanDave

Hmmm. Sounds like that may also be a problem. I have been slowly losing coolant. No sign of water inside the cab though.

Any way to test just the heater core? Or is this one of those things that you have to tear apart the dash to get to it and just replace it while you're at it?

Jay351

You have to tear the whole dash out.. its like the first part they put in the stupid cab. Not fun!

DupermanDave

when the heater core leaks, and it's not dripping anywhere...where does it go?

Can the heater core be fixed? Can the leaky spot be patched up rather than replaced? All the heater cores I'm finding are $100+, and I'm about to order tires. I think I need tired more than a (new) heater core this winter. Can it be patched with some sort of heat resistant plumbers putty or some solder?

Jay351

It can be vaporized into the heater ducts.

You cannot repair a heater core... and its not something you wanna do twice. Replace with a nice new part. Don't cheap out, tires can wait another week or two...
Its like a mini radiator, the damage is usually inside.

DupermanDave

that's what I saw two months ago. Running on the spare tire now, which is more bald than Terry Bradshaw. It's gonna pop any day.

Jay351

ooo, thats no good.

Well its up to you. You can just bypass the heater core in the engine bay. It will leave you with no heat but it won't leak...

p.s terry bradshaw

DupermanDave

So the coolant loss/smell is most likely the heater core leaking and the thermostat is probably causing the temperature gauge problem

What's causing the coolant to overflow and gurgle when I try and burp it after only 30 seconds?

4Crawler

iTrader: (3)

One possible cause is a head gasket leak, engine compression forcing its way into the coolant and pressurizing it. Two tests to confirm this would be to put a pressure gauge on the radiator and see if the pressure rises with engine RPM. Or you can pick up a chemical test kit at Napa to test for exhaust gas contamination in the coolant.

DupermanDave

Grrr. Better not be the head gasket. That's the first thing ever replaced on this truck when I got it a year ago.

How much should I be expecting to pay for a heater core?

DupermanDave

got some new and important info. Just went to idle the engine for about 15 min and get it to normal temperature. After about 15-20 minutes I checked the upper rad hose: it was hot. I then checked the lower hoses (below the alternator) and they werent hot at all.

Could this mean the thermostat is stuck closed?

Jay351

Could be. Or there is an air bubble in there thats causing problems..

DupermanDave

well, i dont know whats going on. maybe i should stop providing information and let you guys guess. I took the truck for a drive to town and it was fine with the temperature gauge. turned the hot and cold air on and couldnt get the coolant smell back.

my truck is possessed.