Overcooling

So here is another overcooling thread. I have a 90 cherokee straight 6 I replaced alot of the cooling system last winter, OEM t-stat. My engine is not warming up when its cold outside and this affects my heater operation, yes I have burped the system, I have a cracked exhaust manifold. My question is could a cracked exhaust manifold cause this overcooling, I was told by an auto shop that they are 2 seperate issues, but I don't really buy what they told me. What do you guys think?

compleetley seperate issues. when i had a cracked manifold it was just noisy.

Ok so its cooling then

So what could be the cause of the engine overcooling and not heating up when it is colder outside. It will heat up to full 210 when its idling, it takes awhile, but as soon as I start driving the temperature drops

How cold is "cold" outside. Thermostats are cheap, I've seen them go bad after a single season, stick open and the motor never warm up properly.

If its -20°F (I really don't know the actual figure, but really really cold) even the thermostat being totally closed the motor might NOT warm up completely. This is where you see people putting covers, blockers over their radiator to help the motor warm-up. If no other drivers in your area are putting blockers, covers on their radiator, then I would suspect that something is wrong with the cooling system, most likely the thermostat.

Change of seasons is when you notice a bad thermostat, it gets in a rutt, opening and closing a certain distance again and again that it sees in summer, then when winter comes and it has to close farther than it has the last 1000 times, it fails.

Remember the thermostat only blocks the outlet to the radiator, NOT the inlet, that remains open always. Of course blocking just the outlet will pretty much cut off the flow to the radiator; BUT in extreme cold, enough of the cold coolant in the radiator will get sucked into the motor and mix enough to keep the engine cooler than the thermostat is set at.

I cracked exhaust manifold, if you have EFI and an O2 sensor, and the crack is upstream or near the O2 sensor, will cause the motor to run very rich (the O2 sensor senses the oxygen leaking in with the air leaking into the crack exhaust, extra oxygen means your running lean and that tricks the ECU into thinking it has to add more fuel to get back to normal). Running rich can make less heat than running normal or lean, BUT, your cooling system should be able to easily adjust, unless you're in EXTREME cold.

actually 53 degrees out

Yea, 53°F should only take a few more seconds to reach operating temp than a summer day.

Most likely problem is the thermostat, even though its less than a year old. Considering how cheap they are, I'd just get a new one with a gasket and replace it and see it solves the problem. If we're wrong, you've only wasted a few bucks and minutes replacing it.

ok how would I fill the system back up, it's a closed system

Sorry, I have an Open System (pressure cap on the radiator), never had a Closed System (pressure cap on the reservoir). I'm sure there is a procedure in the manuals.

I've found with the open system, if I pull the highest heater hose and hold it above the motor, it lets air escapes as the system fulls with fluid, this speeds it up and gets more into the system, then reconnect it once coolant starts to flow out of the heater hoses. This might work for a closed system, BUT get the advice from a manual or someone with a closed system that knows how it works.

megabyte5689 said:

So here is another overcooling thread. I have a 90 cherokee straight 6 I replaced alot of the cooling system last winter, OEM t-stat. My engine is not warming up when its cold outside and this affects my heater operation, yes I have burped the system, I have a cracked exhaust manifold. My question is could a cracked exhaust manifold cause this overcooling, I was told by an auto shop that they are 2 seperate issues, but I don't really buy what they told me. What do you guys think?

Click to expand...

man...i wish i had the problem of over cooling. i live in 130 degree weather and no matter what, i cantseem to get my jeep to cool down, let alone over cool

ok any advice from someone on a closed system

have you flushed the heater core?

i did mine and a brownish orange sludge came out.

now the heat is HOT!!

No, how would you flush it? This still wouldn't explain the engine not warming up to operating temp

Go to shucks and get a powerflush kit, its basically a t barb that you put in your heater core hoses that you can connect a garden hose to. You run the engine with the radiator open and the hose on and see what comes out.

Try searching burping a closed system or bleeding air out of a closed system or something along those lines.

-Alex

I made the mistake once of drilling a hole in the thermostat as recommended here to help the system "burp." Was that a mistake. It would take forever to warm up. It sounds to me like you have a thermostat issue which is a cheap and easy fix.

I've got the same - won't warm up in moderate weather. It does have a three core radiator, open system, and the '92 up heater control. I'm thinking the cheapest thing is just replace the stat with a higher quality one - or run it a gallon less.

I'm just going to pay a shop to fix the issue this time around, I spent countless days last winter trying to fix it and nothing happened

Ok so I forgot to add I can distinctly hear the thermostat clicking when it is opening up and can see the coolant draining from the tank to go in the engine. I forgot to put this because I remember hearing it last year. IT does warm up when it's in park, but not to the full temperature, and the heat does warm up with the temperature, but as I said the engine does not warm up all the way so the heat from the heater suffers, what could this light clicking be, it only happens when the thermostat opens, and when the coolant leaves the tank to go into the engine

megabyte:

My 89 Renix had a similar situation last summer. I actually found that a temp sensor was bad....replaced it, and the system continued to run normally, but the temp gauge worked properly.

Burping a closed system is rather easy. With a cold motor:
1. Fill surge tank with coolant
2. Start motor, turn on heater
3. Remove temp sender (drivers side of the head, all the way in the back)
4. Wait. When coolant comes out from the temp sender hole, put it back together.

You can do this with the surge tank lid on or off. I usually do it with it off, so I can see it and add water as necessary.

*edit*

To flush the heater core, remove the lines going into the firewall. Don't twist or pull them off, take a razor blade and slice the lines off so you don't break the lines inside the heater core. Using a garden hose, pour water into one line, and watch it come out the other. When the water flows out clear and clean, switch hoses to flush it all backwards. Then do it forwards 1 more time.

I've also seen folks mix a solution of 1 part CLR (or lime-away, etc...) to 2 parts water. Put it into the heater core, and let it sit for 5-10 minutes. That can help break up some of the scale that builds up inside the heater core. Flush as needed afterwards.

I'll have to admit to this problem too. Temp comes up, but very far on the gauge. Heater never blows real hot air, even after driving for an hour, or sitting for a long time. I should have replaced the thermostat when I replaced the radiator, so this is likely my fault!!!

Anyway, it does get warmer inside than before, I flushed the block and heater core, there was a load of scaly crap in the heater control valve. I replaced tha radiator and hoses. I probably should have replace the stat and the pump while I replacing the headgasket, but was shortsighted with other problems...

Just concerned now it isn't getting into closed loop.