Low Engine Temps

[87manche]

I have the same problem, with the same closed cooling system.
I've replaced most everything but the water pump and the rad itself.
I'm on the 4th thermostat in a year, from the $3 stants, to the $12 HD stants and a dealer one.
My junk still runs at 190 in the summer, and 170 when it got cold.
The bottle and hoses have been replaced, I tried another cap.
I just hillbillied it up and put a piece o cardboard on the grill. Blocking 75% of the grill and now t heats up quicker and stays at 195 again.
It was the easiest solution, might not be "right" but it works.

 

[Jess]

Could the heater core being blocked cause the temp to not go to 210? It seems to me that if it were blocked it would cause poor circulation and run hot......not cold. The lower hose running to the core is so hot I cannot hold onto it, but the hose on top is only luke warm---I would assume poor circulation to be the culprit.

 

[langer1]

What about a over lean mixture? Less fuel burnt, less heat generated.
Now don't forget I said "Heat", not temperature.

A lean mix = Higher combustion temperature but less heat BTU hr

 

[Jess]

What about a over lean mixture? Less fuel burnt, less heat generated.
Now don't forget I said "Heat", not temperature.

A lean mix = Higher combustion temperature but less heat BTU hr

I would assume I am running overly rich as opposed to overly lean. I am getting about 10 mpg running 215's. I get better than that on the trail rig with 35's. I believe my cat is bad because I am starting to get the rattle.

I thought my poor fuel economy was due to a stuck t-stat, but after changing the 6 month old OE stat yesterday for another OE stat, I know that was not my problem.

The tranny lines were leaking at the connections for the rad, and I thought the tranny fluid restrictions could be playing a part of the low temps, and also fixed that yesterday---with no changes.

 

[Rust Heap]

Could the heater core being blocked cause the temp to not go to 210? It seems to me that if it were blocked it would cause poor circulation and run hot......not cold. The lower hose running to the core is so hot I cannot hold onto it, but the hose on top is only luke warm---I would assume poor circulation to be the culprit.

If you cannot hold your hand on it for over 3 full seconds it is over 150 degrees. Its the ghetto way of checking temp at work when we are too lazy to grab the infrared gun.

Poor circulation = overheat ALMOST all the time. If it is not circulating in the engine properly it will not have enough area to pull heat from. I'd say get a temp gun and check the temps on the engine in various spots while running, maybe there is some spot not getting any coolent and is very very hot.

 

[Jess]

If you cannot hold your hand on it for over 3 full seconds it is over 150 degrees. Its the ghetto way of checking temp at work when we are too lazy to grab the infrared gun.

Poor circulation = overheat ALMOST all the time. If it is not circulating in the engine properly it will not have enough area to pull heat from. I'd say get a temp gun and check the temps on the engine in various spots while running, maybe there is some spot not getting any coolent and is very very hot.

The spots where air bubbles will gather is usually in either the rear of the head, where the temp sensor is, or in the heater core. These are the highest points in the system. If this is the case, I would either be showing very hot on the gague or have very good heat blowing inside. I have neither.
I believe my poor mileage is caused by the engine not reaching proper operating temps, because before this problem developed I was consistantly getting 20+...even towing.

Could a faulty water pump cause this??????

 

[87manche]

I know that since I've ghettod up my rad I get much better mileage, due to proper engine temp.
I can't imagine that a pump would cause it, and I haven't replaced mine yet.
I've never heard of a faulty pump causing low temps, just overheating due to lack of flow.

 

[Jess]

I know that since I've ghettod up my rad I get much better mileage, due to proper engine temp.
I can't imagine that a pump would cause it, and I haven't replaced mine yet.
I've never heard of a faulty pump causing low temps, just overheating due to lack of flow.

just a thought. I am running out of ideas.

 

[Blue XJ]

I'm gonna put some plastic under the cap and screw it back on tomorrow, I can't find a replacement cap at any of the parts stores. I'm still leaning towards an air bubble, even after replacing this last thermostat it seemed like more fluid leaked out then what I put back in. I filled the coolant bottle up and it never really went down, but I would assume when the t-stat was out, the bottle went empty, the upper hose went empty and the front half of the head went empty. I did loosen the temp gauge in the back of the head while it was running and coolant came out, along with a temp sensor in the t-stat housing, so I'm not sure where else the air could be.

I've also noticed my mileage has gone down since it isn't running at full temp now too. I just thought it was because I am always getting into the throttle with the stroker, but even under normal driving its lower.

 

[Jess]

I'm gonna put some plastic under the cap and screw it back on tomorrow, I can't find a replacement cap at any of the parts stores. I'm still leaning towards an air bubble, even after replacing this last thermostat it seemed like more fluid leaked out then what I put back in. I filled the coolant bottle up and it never really went down, but I would assume when the t-stat was out, the bottle went empty, the upper hose went empty and the front half of the head went empty. I did loosen the temp gauge in the back of the head while it was running and coolant came out, along with a temp sensor in the t-stat housing, so I'm not sure where else the air could be.

I've also noticed my mileage has gone down since it isn't running at full temp now too. I just thought it was because I am always getting into the throttle with the stroker, but even under normal driving its lower.

I never saw what year your Jeep was, but if you have a temp sender in the t-stat housing I assume it is a HO. If you put anything under your rad cap it will block off your expansion bottle and with an open system you cannot do that or you will blow a hose or bust your rad or even worse blow the head gasket. The open system should "burp" itself. The burping is only important with the closed system (Renix style).

 

[Blue XJ]

Its a 90 with the closed system, I am just running a stroker motor with a HO head and t-stat housing. I have an Autometer temp gauge attached to the tstat sensor.

 

[Mopar500]

I'm sorry to bring up an out of date thread, but it is rare that I have some input on an issue.

Up until yesterday, I had all the same issues you were having. And, in my case:
Running cold = stuck open thermostat
Replaced thermostat = running hot
Replaced partially clogged radiator = A.O.K. temperature

Bad mileage = tire pressure at 20psi (I don't know how that happened)

You may have a cluster of problems like I did.

 

[Blue XJ]

Anyone else have ideas? New thermostat and a new cap didn't do anything for me.

4.6l motor with 2500 miles
GDI 3 core radiator - 3500 miles on it
heater core - 400 miles on it
thermostat # 4 or 5 - 200 miles on it


everything is new

 

[n1ywb]

You didn't mention how cold it is outside? When I lived in Vermont I would often have to block the airflow to my radiator with cardboard to get it to come up to temp during the winter. I see you are in michigan and it was march when you last posted so presumably it is pretty cold there. In cold enough weather, even with the thermostat fully closed, everything still radiates enough heat to keep the engine running below normal. Especially if you have an upgraded cooling system like I did (or if your cooling system just works good unlike most people's). That little air hole in the thermostat just flows too much coolant. Also the heater core and the air around the engine, in that kind of weather you can practically air-cool the 4.0.

One time it got down to -38F and that was the only time my old cherokee wouldn't start due to weather.

 

[dutchjeep]

Blue XJ, for what it's worth, I had something similar. Two t-stats in a row (both 195 degrees; one stant, one MrGasket) gave me low temps (160 freeway). I got my third t-stat from the dealer, and voila....temps have been great ever since (http://www.naxja.org/forum/showthread.php?t=911599). Just another $0.02.

 

[Blaine B.]

Flushing the heater core - I'd just remove both heater hoses from the water pump and thermostat housing and LIGHTLY flow a garden hose through the heater core. if you see water coming out of the other hose (make sure the heater valve is opened though) you know there is flow through your heater core.

I wouldn't recommend blasting the heater core or you might loosen up some old crud and end up with a leak that will cost you alot of time, as the entire dash must come out to replace it.

 

[Blue XJ]

Flushing the heater core - I'd just remove both heater hoses from the water pump and thermostat housing and LIGHTLY flow a garden hose through the heater core. if you see water coming out of the other hose (make sure the heater valve is opened though) you know there is flow through your heater core.

I wouldn't recommend blasting the heater core or you might loosen up some old crud and end up with a leak that will cost you alot of time, as the entire dash must come out to replace it.

The heater core is brand new as well.

I did the cheap conversion to an open system and just added a radiator filler neck in the upper hose, when I cut the hose in half, there was no coolant in it. Now that all the air is gone, it runs like a champ, my mileage even went up 6mpg!

 

[Blaine B.]

Up 6mpg? How the hell?

 

[Blue XJ]

Up 6mpg? How the hell?

Its no longer running in open loop because the engine gets up tot he proper temp now. When it runs in open loop it bypasses the O2 sensor and adds extra fuel in, no it doesn't.

 

[streetpirate]

The heater core is brand new as well.

I did the cheap conversion to an open system and just added a radiator filler neck in the upper hose, when I cut the hose in half, there was no coolant in it. Now that all the air is gone, it runs like a champ, my mileage even went up 6mpg!

huh?

the upper rad hose had no coolant?
im having the same problem on my 87, new surge tank, thermostat, cat power water pump, runs 190 stopped and 160 moving. 40* outside or so. fails emissions hc 200(allowed) mines 236, and co is six times legal limit.