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I am having problems with my 99 Duratec and I hope someone can lead me in the right direction. During warmer outdoor weather my cooling system acted normal (somewhat). The car would cruise at 190F and while idleing would get hotter until the fans kicked on at approx 212F The temp would then drop off to approx 198F and this would cycle back and forth like this . At highway speeds the car would maintain 180ish degrees, all normal except for some reason I thought engines ran cooler at idle instead of hotter. All besides the point. The issue at this point in time is this. Once the outdoors temp went below 25F the car will get up to temp only while driving. As soon as I come to a stop, I can watch the temp gauge drop from 1/3 of the way up to just at the cold mark. This happens in a a matter of minutes. I verified the actual temp drop with my scantool. I do have heat, only not quite as hot as it used to be. I changed T-Stats numerous times last year to get a steady gauge and heat, and it finally ran fine last winter thru summer. Then I though change the o-flow cap. As a matter of fact I changed the temp sensors last year also. This morning I ran the car for 40 minutes and opened the hood and squeezed the upper rad hose while it was hot. What was odd was I was able to squeeze the hose as it had some give to it. Prior to that after running the car, anytime I grabbed that upper hose it was hard and pressurised like a rock, but not now. Does this sound like a lack of 16lbs of pressure to anyone? I ordered a new degas bottle as the fluid level sensor had been flakey. Could this be a pinhole in the o-flow bottle that might be causing this? The degas bottle was bought as a Christmas gift so I cant get it until then. I just seem to think that it is losing/not maintaining pressure. I also replaced the water pump last year. The car dosent seem to be loosing coolant. I had an uoa done last year and that was fine. If it was a leak I would have at least thought I would be able to hear a hiss (If it was the degas). I dont have the cash right now to get it pressure tested. What is everyones take on the cause? In addition, after I refilled my coolant sytem, I leave the cap on when I test it. Is it proper to laeve the cap off after you refill your coolant system or put it on, then run it till you get it to proper operating temp?
 

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I thought engines ran cooler at idle instead of hotter.[/b]
Engines will run cooler while driving. The water pump at idle isn't flowing as much coolant at idle then if you were cruising on highway. Not to mention there's no air flow through the radiator when stopped, unless the fans come on.

one question I have is what kind of thermostat did you put in (aftermarket or Ford)? If aftermarket I'd recommend getting a ford one installed. I've never had much luck with aftermarket thermostats. Not to mention I've seen quite a few that stick open after a short period of time.

As for leaving the cap on or off after filling degas bottle, you can put the cap right back on if you're just topping off the system. If you're doing something to the cooling system like a T-stat, water pump, etc, that lets air into the system, then you'll want to leave the cap off till the T-stat opens. But for just adding fluid, you don't have to worry about leaving the cap off.
 

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It is the job of the t-stat to maintain a minimum temp. So that looks to be the problem.

With the advent of the degasser bottles the small hose that comes from the head purges any air out of the system. Fill it to the top. The after a complete heat/cool cycle fill it to the top again.

Anytime the cap is taken off when the system is hot it will need topped off again when it cools. It is important to completely fill the bottle and do not go by the cold/hot level marks.
 

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It is the job of the t-stat to maintain a minimum temp. So that looks to be the problem.

With the advent of the degasser bottles the small hose that comes from the head purges any air out of the system. Fill it to the top. The after a complete heat/cool cycle fill it to the top again.

Anytime the cap is taken off when the system is hot it will need topped off again when it cools. It is important to completely fill the bottle and do not go by the cold/hot level marks.
[/b]
Well, you don't want to fill the bottle completely when it's cold tho, or when it heats up and expands, there's no room.
 

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<div class='quotemain'>
It is the job of the t-stat to maintain a minimum temp. So that looks to be the problem.

With the advent of the degasser bottles the small hose that comes from the head purges any air out of the system. Fill it to the top. The after a complete heat/cool cycle fill it to the top again.

Anytime the cap is taken off when the system is hot it will need topped off again when it cools. It is important to completely fill the bottle and do not go by the cold/hot level marks.
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Well, you don't want to fill the bottle completely when it's cold tho, or when it heats up and expands, there's no room.
[/b][/quote]

i remember something on the board here about ford releasing a tsb to actually fill the bottle all the way up to the top.
 

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i remember something on the board here about ford releasing a tsb to actually fill the bottle all the way up to the top.
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Generally, thats needed when servicing the cooling system to take the place of the air in the hoses (specifically, the one above the tstat).


As for the problem.... What temp is your current thermostat? Its wintertime anyways so i wouldn't put anything cooler than the OEM 190 degree tstat in there and it see if that takes care of the problem.
 

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No Ford recommends filling the coolant tank as full as possible. This is done to minimize the air in the system. Air in the cooling system even if only in the coolant tank will cause chemical reactions and start corrosion. There is nothing negative about keeping the system as full as possible. Any excess will be pushed out the cap. You won't even notice this.
 

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With the advent of the degasser bottles the small hose that comes from the head purges any air out of the system. Fill it to the top. The after a complete heat/cool cycle fill it to the top again.[/b]
well than it is interesting why FORD recommends to install a so-called restrictor in the outlet of that hose that is on the engine (for 96-97 Vulcans).
Mine temp falls when I drive the car, but when it idles temp is stable.
 

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Discussion Starter #9
No Ford recommends filling the coolant tank as full as possible. This is done to minimize the air in the system. Air in the cooling system even if only in the coolant tank will cause chemical reactions and start corrosion. There is nothing negative about keeping the system as full as possible. Any excess will be pushed out the cap. You won't even notice this.
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I saw Fords CD that says keep the bottle full on the duratecs. I am running a Napa 190F stat that i took out of the car in the summer, as I felt the car was a bit too hot. So I dropped to 180F stat for the summer. The stat (190F) was working fine for a winter. And trust me it took a 1/2 dozen or so thermostats to get it right the first time around when I got this car. I cant believe that a stat that sat in a box for a summer after working fine, all of a sudden went south on me. I have heard all the issue with problematic stats before all of this. Even when I went to put a Motorcaft stat in the car ran cooler then it should have, it was the same problem over and over again. I do have heat. once the car has been driven, and it gets nice and hot too. Now when the temp gauge comes down, the heat dosent seem to be affected. I am wondering If maybe a flaky sender (temp) that gets goofy at the colder ranges. The next big thing I dont like is the stant radiator caps, as opposed to the Motorcaft caps. My original cap would only let you tighten it so much and then click so you couldnt turn it anymore. The stant cap lets you tighten that cap as far down as you want, which can ruin the inner seal, as well as cracking the top of the bottle. Now, If I let the car run say 30 minutes, the car temp will stabilze much better, witout any drop. The temps (outside temps are into the 20s today). But I do eventually get good heat. I just wish that gauge would stabilize in the cooler weather. Once the outside temp gets to above 35F the temp will come up and stay put.
 

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Now, If I let the car run say 30 minutes, the car temp will stabilze much better, witout any drop. The temps (outside temps are into the 20s today). But I do eventually get good heat. I just wish that gauge would stabilize in the cooler weather. Once the outside temp gets to above 35F the temp will come up and stay put.
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I have this problem too, at times, it'll be just above the cold normal mark, to about 1/3 of the way up (160 t-stat) when driving around. No idea why, since I have the fans on constantly due to my HVAC settings, and don't change speed much on the highway.

At idle it's worse. WIll go from just under cold normal to 1/2 way up.

Always have heat though.
 

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I put a restriction the line that comes off the heads into the degasser tank on my SHO. I feel it lets too much coolant bypass the engine as the coolant coming out of that hose (on the SHO and Duratecs) is coming almost directly from the t-stat blending of coolant from the lower hose. By putting a restrictor in that hose this forces more coolant to go down into the block on the passenger end of the block.

The factory t-stats that run at ~190F are the best for the engine.
 
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