This is prob a stupid question but here goes: are you sure the thermo is facing the right way? I know they will fit backwards, but dont know if the results would be the same as far as cooling.

 

It wouldm't open in reverse...Would it? But he's still getting normal temps. at idle, which is the confuser.

 

The thermostat is in the right way, 12:00 position. there is heat in the cab now, ample amounts, however the engine temp is still in the low range with the needle below the N, at idle and hiway speeds. The dealership flushed the system of airlock and replaced the temp sending unit. There is pressure in the system now but still low engine temp. I replaced the radiator cap(16lbs) and was told by the guy there that maybe the clutch fan was running at high speed all the time and to replace that next. This truck only has 38000 miles on it. Must have been parked alot. Is it possible the silicone ring is not doing what it should? He said it could go either way. Told me to put cardboard between the radiator and the a/c to see if that helps. It did and now the temp is almost to the middle. I suspect the fan is turning at high rpms and that's why I'm getting bad gas miliage. The fan turns so fast at start-up you could blow dry your hair under it! That would explain why the engine doesn't get a chance to warm up. Any thoughts on this? Could it still be the waterpump maybe?

 

I think I'll replace the waterpump too, since I'll have access to it when changing out the fan. Won't be able to work on it until this week-end so I'll post then.

 

I still wouldn't rule out a faulty gauge, get your truck up to operating temperature and remove the cap and insert a candy or cooking thermometer in and see if the temperature is at what your thermostat rating is i.e 185* or 193* etc.

 

Even if the fan was running at high speeds it still won't cause this! Older trucks never had the clutch type fans, the clutch is there to reduce drag on the motor and save gas mileage, and it's not needed when traveling down the road. You would have so much air coming through the rad the fan wouldn't make any difference one way or the other! The thermostat keeps the coolant inside the engine until it reaches a preset temperature. Also if the pump was bad your engine would be over heating, and you already know its circulating so we can assume the pump is ok. So there could be 3 things going on here.
1) Bad gauge but I don't think so.
2) Bad thermostat stuck open or opens too soon.
3) Thermostat too low of a temperature.

Pretty much it, if you can keep the coolant in the engine long enough its going to get hot, and the longer that thermostat stays closed it doesn't mater what the hell your fan is doing, its going to get hot.

It's a very simple system, that's where your problem is. See when a thermostat fails to open your engine will over heat big time and it wouldn't mater how great of a rad you have or how big of a fan you had, coolant will not circulate and its just going to get hotter and hotter.

Therefor I conclude your coolant is circulating before it reaches the desired temperature, or the temperature you think it should reach.

 

Okay, I only suspect the fan because of my low gas mliage. However we live in a cold climate and if the water pump isn't circulating correctly (weak pump) then would it be circulating cooler water ? The top half of my radiator is freezing cold. Also I can hold the hoses without any discomfort. I would suspect when it's hot in the summer I'de be getting the opposite problem. And what about the cardboard working?

 

Cardboard is only going to try and do what the thermostat should be doing, but with less control. The ideal of the thermostat is to regulate the temperatures cardboard can not do that. Also if your pump wasn’t pumping you would have the opposite effect, it would run hot.


I would get another thermostat and one that is at a hotter temperature than the one you have now. I would also get a name brand thermostat, for some reason the name Gates comes to mind.<O</O

If you watch your gauge you should almost be able to tell when the thermostat opens, For example I just replaced mine but its too cold but I can watch the gauge and it will go up to the “O” in normal and when the thermostat opens it drops to the “N” My factory thermostat ran around the “M” in normal and gave me good warm heat, right now I only get slightly warm air and it really doesn’t warm up the truck at all. So I think I’ll try a 194 this time.<O</O

Now before this thermostat I used one of those failsafe and it failed in the open position and the truck would not warm up at all. <O</O

 

Yep, that's what it does. I can see when it opens and the needle does drop before it gets warm. The new thermostat I used is Prestone 306-195. And why am I getting good heat in the truck now?

 

Good heat sitting? or good heat when your going down the road? If you have good heat than I wouldn't worry about it.

 

Well, they can sell them cheaper if they make them cheaper, and they can make them cheaper by using poor quality stuff.

 

Jet, your pump prob didnt have enough poop left to circulate coolant all the way to heater core, thru thermo and heater valve. The veins can wear down. So the new pump moves the fluid much harder and faster. I've also seen plugged heater hoses, crimped hoses, plugged cores, heater valves corroded shut/open. Make sure the thermo is installed the right way, (look for printing on one side that says: this side towards engine/radiator.

 

[QUOTE=bossind]...the gauge...will go up to the “O” in normal and when the thermostat opens it drops to the “N” My factory thermostat ran around the “M” in normal and gave me good warm heat, right now I only get slightly warm air and it really doesn’t warm up the truck at all. So I think I’ll try a 194 this time.<O</O[QUOTE]

When I bought my Bronco I livede in Florida and it was very hot. The temp gauge would barely make it to the first line, before the "N." Being in Florida, I was pleased with this. If I let it idle for a long time, it would crawl up to around the "R."

I do not know what the temp of the t-stat that was in the Bronco was when I bought it, but when I moved to Colorado I could not get any heat in winter. It would not even get to the first line on the gauge. That's not good, and then consider the need for a defroster as well, so I definitely neede to fix it ASAP. I went to NAPA and asked for the correct temp since I didn't know what it was and they sold me the 194. Apparently that is what it came from the factory with.

That solved the problem I got plenty of heat. I was worried about overheating in the summer with the AC on. It gets over 100 degrees here a lot in the summer. But come summer, everything was cool (pun intended).

Now that I have the correct t-stat I can see how it is really supposed to go. Normal operating temperature is a little less than halfway on the gauge, a little bit before the "R." Then it stays there, but oddly enough it goes up and down, like in a cycle; It won't go above operating temperature, there is never a threat of overheating, but it constantly goes from the "R" and down to almost the "N" and then back up, etc. etc. It's done this over two different t-stats, three different tremperature sending units and I have heard others say the same thing. I don't worry about it, it's just strange. My truck has never come close to overheating, and it has good heat into the cab. I don't worry about it.

Back in Florida, I used to be concerned about the needle rising at idle. I thought that there was something weak in the cooling system, but it never overheated. However, now I can see that the truck was trying to get to operating temperature, and that the low temps were because of the T-stat.

A normal sequence of events for a 1990 5.8 automatic trans truck is this:

1 - Start the truck from cold. The t-stat should be closed at this time if it is working correctly.

2 - Depending on the outside temperature (as to how long this takes), the needle on the temp gauge will slowly start to climb. Obviously, it will climb slower if it is very cold outside, but it still should reach operating temperature. It will keep climbing until the t-stat opens. You may watch your temp gauge go as far as 3/4, or possibly more, and then suddenly the temp will drop way low and then climb a little bit as the truck stabilizes and settles at operating temperature. Like I said, operating temperature is somewhere between 1/3 and 12 of the gauge. NOTE - sometimes in very cold weather, the gauge will show a hotter than normal temp. I've seen mine go about 1/3 higher before the T-stat opens in very cold weather. I am not sure why this occurs. But don't freak out if you see this - just keep an eye on the gauge and as long as it eventually goes down and does not overheat you have nom problem and the truck is behaving normally.

3 - The temp should no longer raise. Once at this point, my gauge does not move even if I am climbing and the outside temp is very high. But if it rises a little in these conditions, but never overheats, then you should look into the cooling system. The first thing to do would be a good flush and fill with clean coolant and a new radiator cap. Also, make sure the timing is correct. Incorrect ignition timing can cause a vehicle to run hot too.

 

PS - I know that your problem is not with overheating, but the point is the same -- to have the cooling system work properly.

 

Thanks everyone. I think I just couldn't believe the stat was again bad, but if mine is stuck open as was explained, I can see this happening in my truck. It's below 0 today and sure enough the heat output sucked . I'm on my wat to the dealership to get a decent one. Hope it works.