Bad Thermostat? Heater Core?
Hey, so, I don't know if it's normal, but I think I have somethin like that happening. I can drive my monte for like an hour and the blower might have a little heat! Could it be a thermostat?? if so what does it take?? I have a friend who might be able to help if I can get the info!! Thanks everyone!!
im guessing the engine temp is pretty good, it's always under the halfway marker by a couple ticks, figure that needle has mor travel it could go so i'm doin' alright not overheatin.
just checked the raditor and it seemed good. i even tried to pour some antifreeze in and it spilled out almost as soon as i poured. so i dont think im loosing antifreeze.
just checked the raditor and it seemed good. i even tried to pour some antifreeze in and it spilled out almost as soon as i poured. so i dont think im loosing antifreeze.
Monte Of The Month -- August 2012
Joined: Apr 2011
Posts: 6,074
From: Seattle
2004 Monte SS
I live in the midwest where it's about 15 degrees today. I drove home about 30 minutes and the whole way home my engine temp said 185 (normal) and I had good heat within the car. After I got off the interstate I rolled my window down real quick and my hands got cold. I turned my blower on high and that's when things got weird. The blower spooled up with heat, then it gradually got colder and colder. At the same time the heat was getting colder and colder the engine temp was rising, eventually settling on about 225. I turned the blower back down, the heat got very hot again, and the engine temp went back down to 185. When I got home I tried to repeat it in the driveway, I couldn't do it. I turned the car off, let it sit 30 seconds, turned it back on, and now, no matter what blower speed, the air temp is moderately lukewarm, certainly not real hot.
It sounds like a typical thermostat failure, but I'm having trouble rectifying why my engine temp went up and the heat went away. Would a bad heater core show itself some other way?
I live in the midwest where it's about 15 degrees today. I drove home about 30 minutes and the whole way home my engine temp said 185 (normal) and I had good heat within the car. After I got off the interstate I rolled my window down real quick and my hands got cold. I turned my blower on high and that's when things got weird. The blower spooled up with heat, then it gradually got colder and colder. At the same time the heat was getting colder and colder the engine temp was rising, eventually settling on about 225. I turned the blower back down, the heat got very hot again, and the engine temp went back down to 185. When I got home I tried to repeat it in the driveway, I couldn't do it. I turned the car off, let it sit 30 seconds, turned it back on, and now, no matter what blower speed, the air temp is moderately lukewarm, certainly not real hot.
It sounds like a typical thermostat failure, but I'm having trouble rectifying why my engine temp went up and the heat went away. Would a bad heater core show itself some other way?
As Jason mentioned, the sludge in the radiator could be from lack of maintenance. The first thing I would do is a pressure test on the cooling system and/or a cylinder leak down test to eliminate the possibility of gasket failure. If failure is not evident then I would remove the old thermostat (replace the thermostat housing) and do a reverse flush on the cooling system. If there is a blockage in the heater core this will usually clear it out. Install a new thermostat and refill the system making sure all air is purged from it.
Joined: Jan 2014
Posts: 138
From: Washington, DC
As Jason mentioned, the sludge in the radiator could be from lack of maintenance. The first thing I would do is a pressure test on the cooling system and/or a cylinder leak down test to eliminate the possibility of gasket failure. If failure is not evident then I would remove the old thermostat (replace the thermostat housing) and do a reverse flush on the cooling system. If there is a blockage in the heater core this will usually clear it out. Install a new thermostat and refill the system making sure all air is purged from it.
When someone does a pressure test, how does that show gasket failure? I thought the pressure test only showed leaks in the radiator, or is there a different way to check pressure instead of the good ol fashioned cap with pump assembly shown below?
I think my LIM is failing on it, but I'm scared it might be the head.
Monte Of The Month -- August 2012
Joined: Apr 2011
Posts: 6,074
From: Seattle
If there is a leak in the gasket between the cylinder and a water passage air can be heard escaping from the spark plug hole. If there's a leak between a water passage and oil passage air can be heard escaping into the crankcase. A cylinder leak down test is a far better way of doing it, but most DIYers don't have access to the equipment to conduct one, so you do what you can with what you have. A loaner pressure tester from the local parts store is much easier to acquire. 
Joined: Apr 2010
Posts: 12,590
From: Mentor, Ohio
FYI - From my experience....
If you have a bad LIM gasket, a radiator pressure tester will almost always (in my experiences it always did), exploit that problem (air/coolant normally bubbles to the outside of the engine).
Now, with head gaskets, I did have a failed head gasket causing me a bunch of problems on a 3100 engine. Every single time I put pressure on the cooling system with the tester, it never dropped. I put the tester to the max pressure for the rad cap. A couple of times, let it sit for an hour and it never lost one bit of pressure. In that situation, the cylinders were forcing compression gases into the cooling system via a crack in the head gasket, causing an air pocket in my cooling system and to over pressurize the system and temp gauge to read all sorts of crazy readings.
When you turned the car off, because the cylinders put so much pressure in the cooling system, it blew out the rad cap and even back into a cylinder (causing some short lived rough idle and later as it got worse a moment of big white clouds from the exhaust).
When I finally got some input confirming head gaskets, I tore it down and sure enough, bought head gaskets had a crack that only showed if you twisted the gasket and it went from a coolant jacket to a cylinder.
If you have a bad LIM gasket, a radiator pressure tester will almost always (in my experiences it always did), exploit that problem (air/coolant normally bubbles to the outside of the engine).
Now, with head gaskets, I did have a failed head gasket causing me a bunch of problems on a 3100 engine. Every single time I put pressure on the cooling system with the tester, it never dropped. I put the tester to the max pressure for the rad cap. A couple of times, let it sit for an hour and it never lost one bit of pressure. In that situation, the cylinders were forcing compression gases into the cooling system via a crack in the head gasket, causing an air pocket in my cooling system and to over pressurize the system and temp gauge to read all sorts of crazy readings.
When you turned the car off, because the cylinders put so much pressure in the cooling system, it blew out the rad cap and even back into a cylinder (causing some short lived rough idle and later as it got worse a moment of big white clouds from the exhaust).
When I finally got some input confirming head gaskets, I tore it down and sure enough, bought head gaskets had a crack that only showed if you twisted the gasket and it went from a coolant jacket to a cylinder.
Thread Starter
Joined: Jun 2010
Posts: 174
Alright, I'm jacking my thread back. I was stop and go driving today, my temp started to go up (never higher than 220/230), I lost my heat again and then after about 2 or 3 minutes of this driving I started to smell coolant in the cabin. I couldn't get out of the traffic, but when I got a chance I opened the hood. From just behind (looking from front of car) the upper intake manifold I saw steam rising and the smell of coolant was potent. I also saw, on top of the LIM on that pocket between the head and UIM, something boiling. I presume this was water from the coolant?
Anyway, it was kind of getting dark so I didn't have the best view to anything. I couldn't see well on the back side of the engine so I don't know if I had the same boiling. I need to go to work tomorrow but will have time to troubleshoot this weekend. Do you guys recommend a pressure test, or do my symptoms sound like a pretty common thing? UIM gasket? LIM gasket? Aren't bad head gaskets kind of rare on 3800's?
Further to the point of actually doing the work, what gaskets are considered the best for each of the various locations I could be having failures on? Anything else worth doing since I'll be investing this much time?
Needless to say, I'm super excited about doing this work in my 10 deg F garage. Ugh.
Anyway, it was kind of getting dark so I didn't have the best view to anything. I couldn't see well on the back side of the engine so I don't know if I had the same boiling. I need to go to work tomorrow but will have time to troubleshoot this weekend. Do you guys recommend a pressure test, or do my symptoms sound like a pretty common thing? UIM gasket? LIM gasket? Aren't bad head gaskets kind of rare on 3800's?
Further to the point of actually doing the work, what gaskets are considered the best for each of the various locations I could be having failures on? Anything else worth doing since I'll be investing this much time?
Needless to say, I'm super excited about doing this work in my 10 deg F garage. Ugh.