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Low Engine Temps

does your fan clutch spin freely when it's cold? It should only offer resistance when the coolant temps go up and would provide extra cooling when unneeded if it were turning the fan when still cold????

--Shorty

P.S. mileage would suffer as well.
 
streetpirate said:
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.
Click to expand...

When you give those temps, where are you getting them.

You have three temp sensors, one or all can easly be bad.
 
they are from the factory gauge, the clutch fan might be bad, thats the one thing i didnt think to check.
 
It's well below freezing here and I have had cold engine temps for a while, havn't had a chance to replace the t-stat yet (I barely drive the thing right now anyways).
Anyways, I thought the t-stat might be stuck "open", but I'm not too sure. I don't know much about cooling systems so I thought I'd ask here. My temp gauge barely climbs past 100* at any point, but the engine seems to warm up to regular temps in a regular amount of time. I can start the truck, let it idle for 5 minutes while I scrape the windshield and windows and by the time I hop in the heater is blowing hot air. Does this still mean that the t-stat is bad? I had the same thing happen last year when I bought the jeep in the winter, always low engine temps. In the summer, when it was hot out the engine was getting to 210* without problems. Do I just have a bad t-stat or is something else wrong?
 
Yea, I'm also going to chime in here.

I had some major cold-running problems....The factory gauge would read less than 160 freeway, 90* + outside temp. Now, with a new dealer t-stat, new upper/lower rad lines, and a flushed heater core, things had seemed to have smoothed out a bit.

With the colder temps coming in, I've noticed that my gauge will come close to 210 upon warm-up, then will drop back down to 160-175*. A leaking pressure cap was suggested....is it possible that this could also be caused by a leaking heater hose?? Seems that somehow mine got jacked up during my heater core flushing......it appears to be leaking out of the lower hose, directly from the firewall...

Any ideas would be great, as I've noticed my MPGs dropped off sharply recently. I attributed it to the winter fuel, but it could also have something to do with the leaking/broken exhaust manifold.....

89 XJ, Renix 4.0L
 
Mine dips back down when it's cold like it's been. But after that when it gets up to temp it stabilizes.

Just think of all that ice cold coolant that starts flowing when the thermostat opens even a little bit.....
 
I dont see any way that my temp gauge should be able to read 160 (white mark between 100 and 210) all the time, the 195 stant thermostat i put in 2 days ago should keep that from happening. i dont think my gauge is wrong, because at 160 the air from my heater (which has always worked GREAT) is balls cold.
after driving for a while, i can pull over and let it idle, and it takes 2-3 min to get up to 180-195ish, the heater works better, but not as warm as it used to be.



edit, i do have a small hole drilled in the thermostat for burping, prolly 1/8th hole
 
Last edited:
What if my thermostat is working, my heater plugged over the summer, and my gauge is reading off?
i checked the clutch fan, it turns easily by hand when cold, but is tight enough to not freewheel.
 
Muad'Dib said:
Im interested in this thread as well. Im having very similar problems. Running overly cool with a good t-stat. (on my 3rd)
Would a very small coolant leak cause this?
Click to expand...

Likely not. A pressure leak in the cooling system means that the system is not able to maintain pressure over the liquid coolant. This means that the boiling point of the liquid won't be increased (relative to pressure in the system,) which means that you'll boil over a lot sooner.

You may want to think about a "restrictor" somewhere, to reduce the volume of coolant flow through the system per unit time. It's common enough in racing circles - and part of the job of the thermostat. However, I seem to recall that someone here did a nice writeup (with pictures) of a "coolant throttle" he'd put in the upper radiator hose that seemed to solve a similar problem he was having.

Sadly, I don't have it in my subscriptions listing (which surprises me!) and a quick search isn't turning anything up. I'm fairly sure it was done "pre-crash," so put a bit more effort into finding it (and then email me the URL for it, would you please? I should archive this...)
 
I had the same thing going on, sort of. Mine would either run too cold and/or overheat at odd times. I always thought some of it was poor circulation, the cooler water would pile up in the back of the engine near the temp. gage sensor and the front of the engine would overheat. Somewhere between changing the thermostat and replacing the football it went away. I also had a fairly plugged up radiator, whether that was also a factor, I haven't a clue.
 
no idea of the plugged factor, but ive got a great water pump, about 1 year old, new surge tank (football, heard it called turtle too?) and new thermostat.
ive got to check the resistance on the gauge sender to see if the gauge is way off or not.
 
streetpirate said:
no idea of the plugged factor, but ive got a great water pump, about 1 year old, new surge tank (football, heard it called turtle too?) and new thermostat.
ive got to check the resistance on the gauge sender to see if the gauge is way off or not.
Click to expand...

In order to check resistance you also need to know the real coolant temp anyways using a infrared thermometer.
Be aware the gage can be off also and thats a little harder to fix but if the gage says it's cold and your not getting heat I would say don't worry about the gage right now.
The comment about the turtle is incorrect because the turtle is a dead end, there is no flow across the turtle.
 
langer1 said:
In order to check resistance you also need to know the real coolant temp anyways using a infrared thermometer.
Be aware the gage can be off also and thats a little harder to fix but if the gage says it's cold and your not getting heat I would say don't worry about the gage right now.
The comment about the turtle is incorrect because the turtle is a dead end, there is no flow across the turtle.
Click to expand...
There is a minimal flow through the turtle. Outlet thermostat-inlet turtle, outlet turtle-inlet pump. Depends on the pressure balance in the main engine cooling system and heater system (heater valve). The heater valve doesn't stop the flow completely to the turtle, just diverts most of it.
I may be wrong, but pumps and flow is my trade. It's always possible my assumptions are wrong though.
 
The thing that fixed mine was finally getting all the air out of the system. I bought an inline filler neck and installed it in the upper radiaotr hose (which was full of air to begin with) I figured havign a cap that I could open in the highest point of the system would make it easy to bleed off air.

http://store.summitracing.com/partdetail.asp?autofilter=1&part=CSI%2D971&N=700+0&autoview=sku

csi-971_w_m.jpg


After installing it, I decided to convert to the open style system, since I was half way there.

I eliminated the pressure bottle and heater control valve by running a hose from the tstat outlet to the heater core, then a hose from the heater core back to the water pump.

I attached a 5/16" hose from the nipple on the filler neck and got a pressure bottle from an XJ in the junk yard and connected it.

Since then, the temp has stayed right at 195 and the heat is working good this year so far, but its only gotten down to 25 degrees or so, so far.

I knew it was air trapped in the system, so I figured I might as well convert to the open system to help bleed off the air. Total cost for the conversion was $65 and about an hours worth of work.
 
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