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Temp gauge slow to rise

14K views 35 replies 12 participants last post by  Lgbpop 
#1 ·
Hey fellow members,

I just finished changing the heater core on my '99 sable with floor shift using the shortcut. I didnt see too many people on here talking about using the shortcut with floor shift, but i can say that it is possible. Instead of cutting the metal bracket, I had to cut a horizontal plastic crossmember that supported a bracket behind the ashtray. With that out of the way, there is enough room to slide the core out.

Anyways, I changed the core because I thought it was still plugged with rust even after backflushing it about 6 times. Since I don't have the bypass tube anymore, it dawned on me that the plugged heater core could be causing backpressure and therefore preventing it from heating properly. I proved myself right when I bypassed the core completely. I did this by taking some spare heater hose and "looping" from the lower intake over to the other side into the water pump. With this setup, my temp gauge rose to halfway about three times faster than what it normally did with the core connected.

That being said, I replaced the core with a brand new spectra premium one for pretty cheap. Got everything back together and went for a drive. The temp gauge rose at the same speed as the old core. :angry:

Now I am thinking that it is the core itself and how its designed that is causing a flow problem. Or another possibility could be the coolant itself because when i had the system "looped", all that was in the system was tap water. Every other "normal" time was coolant in the system which is a year old. Could it be possible that the coolant has lost its heat transferring capabilities?

Any input would be appreciated.
 
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#2 ·
Temp rising slowly usually means stuck open Tstat. How slowly does it rise? Do you have a motorcraft thermostat in?

What boggles my mind is that you bypass the core and it rises normally. Did you check if the temp from a scan tool corresponds with the temp the gauge shows?
 
#3 ·
My Vulcan heater core has a bypass built into the system. Supposedly this is to prevent the heater core which is apparently prone to clogging from restricting flow of coolant to the engine. During the "Clinton" flush you are supposed to clamp off the bypass to force flush the heater core. So I am not questioning your observations, just don't understand results. I would look at thermostat but cannot understand how bypassing the heater core allows a quicker warm up?

Scott
 
#4 ·
Make sure the thermostat is facing the right direction,
make sure its not stuck open (DON't USE FAILSAFE STATS!)
Take the water pump off and make sure there are fins left on the impeller
 
#7 ·
Another thing i should of added in the original post. Sorry guys, it was the cuba libres that i had last night :p. Anyways, both the water pump and the thermostat are brand new. The old water pump was in bad shape, so i replaced it. And as far as the thermostat, I have changed it on several occasions. Original thermostat didnt have the little jiggle valve, so i replaced it with a prestone 197 thermostat that did have the valve. I saw no difference, so i bought a $17 motorcraft thermostat. This one also had the jiggle valve, and it also made no difference.

The amount of cooling system related maintenance that i have done to this car is more than i have ever done to any other car.

Im out of ideas to be honest.

Thanks for your replies
 
#8 ·
Okay, well how long exactly are we talking about here to warm up? Give your starting and ending temperatures.

Also, has it occurred to you that eliminating the bypass might have something to do with this? I'm guessing the bypass is there to help speed up engine warm up times in addition to preventing a total blockage in the event of a heater core.

Pure water will conduct heat better than antifreeze (higher heat capacity), which will mean it will take the water longer to heat up than antifreeze. Either way, you should always maintain the proper antifreeze concentration (between 40-60%). You should check your concentration with a hydrometer. The system is not designed to be run with straight water, so that might have something to do with it.
 
#10 ·
Something you need to keep in mind, something I learned when looking for an OEM bypass/heater core assembly when mine had terminal pinholes. The Vulcan engine was designed with cooling jackets in the front and back of the block that are NOT connected internally. This was done to simplify casting the blocks. The bypass part of the OEM bypass/core assembly is the connection, allowing unrestricted flow of coolant throughout the entire block no matter the condition of the heater core.

If your cooling system doesn't include the bypass (in other words, all coolant passes only through the heater core), your engine's operating efficiency and long-term health is being compromised even if the core is perfectly clean.
 
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#11 ·
As you know, my bypass is removed so coolant only passes through the heater core. The core is brand new, so it isnt plugged. And i doubt it will plug because I have installed an inline filter on the heater core inlet hose. This prevents the core from plugging up with rust that is impossible to remove. This filter is easily accessible and cheap to clean/replace.
 
#13 ·
The heater core is not a wide-open hose or pipe - it's a miniature radiator, in which the size if the inlet and outlet are much larger than the passages the coolant passes through to shed heat. In other words, even in new condition the core only allows so much flow through it. By removing the bypass you are cutting down on the coolant flow through the entire system.
 
#15 ·
^^^^ +1

On most modern cars, including the Taurus, the heater core is an integral part of the cooling system, not an "extra loop" just for heating the car interior like it was in the old days. On the Vulcan, flow thru the core is important for cooling the bank 1 (firewall side) head. If the filter plugs up, the rear head will overheat. Vulcans do not like to be overheated!!!
 
#16 ·
Just to let you guys know, my temp gauge still drops periodically from the halfway point to the bottom of "normal". It will then slowly climb back up to the halfway mark. It also seems that when the temp gauge drops, all of the pressure in the cooling system is lost. I wait for it to drop, then i feel the upper rad hose and it is hot but soft. Then i take the cap off the bottle and there is no pressure at all.

I'm pretty sure the Vulcan is the simplest cooling system out of them all. Compare it to the v8 sho, which has the reverse flow design which i don't understand at all.

In the vulcan's simplicity, i still don't understand why the bypass is needed. I think the very early '96s didn't come with a bypass. It was Fords simple idea to throw it in there and solve problems of rust clogging the small passageways in the heater core. I guess they didn't take into consideration that people up north drive these cars, and how important it is to have heat in the winter months.

Think of it this way. Some of you are telling me that the bypass is there to allow more flow for required cooling of the rear bank. Firstly, the size of the hose coming off the lower intake is only 5/8, so it can only carry so much at once. If my heater core is 100%, im pretty sure it can take the flow required for adequate cooling.

I'm really close to giving up on this issue, and just scrapping the car if the engine seizes. I will never again buy a 96+ taurus/sable with the Vulcan engine. Duratec's and sho's from now on.
 
#18 ·
Nothing is perfect. If you followed a few recent duratec threads, there has
been a hole in the oil pan with catastrophic results, and burnt valves and
low compression.

Now, the SHO's are notorious for cam issues if they have not been welded
with also catastrophic results.

The bypass was an add on after early gen3's had cooling issues.
If the heater core plugged up, the coolant flow would be impaired causing
heating issues in the heads.

Your a brave guy if you took the degass cap off with the motor hot
and running. Hope you took precautions. If you found NO pressure there,
you have issues. You just need to find them. Maybe you need to get the
motor hot and stop and turn off the car. Open the hood and listen closely
for pissing or hissing sounds. Look for anything damp or wet.

Your losing pressure somewhere.

you need to step back and retrace your steps.

YOU might want to build one of my ghetto coolant pressure gages and
leave it inserted in the degass lines and try to keep an eye on the pressures.

and you are 100% sure the thermostat is a motorcraft with the jiggle
valve clocked at 12:00, and NOT in backwards?
 
#17 ·
The bypass is really used mostly only used in the beginning of the engine warm up stage until the thermostat opens up. Then the flow is thru the two holes in the the timing cover which has one for each head. Without the bypass there is no water circulation in the engine block because the only outlet is thru the radiator and the thermostat cuts that off when cold.

I left my bypass in place but to get a little more heat in the winter, I put a screw clamp in the bypass hose and tighten it which compresses the hose to force more flow into the heater without totally closing it off. In the spring, I just loosen the clamp.
I believe my 1990 Sable was recalled because of the lack of bypass and overheating. The more flow the more even the temperatures.
 
#19 · (Edited)
Just to let you guys know, my temp gauge still drops periodically from the halfway point to the bottom of "normal". It will then slowly climb back up to the halfway mark. It also seems that when the temp gauge drops, all of the pressure in the cooling system is lost. I wait for it to drop, then i feel the upper rad hose and it is hot but soft. Then i take the cap off the bottle and there is no pressure at all.

I'm pretty sure the Vulcan is the simplest cooling system out of them all. Compare it to the v8 sho, which has the reverse flow design which i don't understand at all.
That makes sense, since the temperature is related to the pressure. Just like a pressure cooker the higher the pressure the higher the temperature. At atmospheric temperature your coolant will boiler just a bit over 212F and can't get any hotter. If you go to the top of a mountain and try to heat food by boiling it doesnt get hot because the pressure is a lot lower. Raise the pressure by 14 to 16 psi which is regulated by the cap the coolant will not boil until over 260F. I might be off on the numbers a little. The trick is not to let it boil since the metal to coolant heat transfer drops significantly and you will overheat.

It works the other way around, a hot coolant system is still functioning but take that cap off and suddenly you have water that is not supposed to be liquid anymore by the laws of physics and flashes to superheated steam. It will burn the hell out of your face and hands.

Get a new Ford cap or have yours tested. It may be venting early or not sealing at higher pressures.
 
#24 ·
I hear you regarding the OEM hose/pipe assembly. I never said it was one of Ford's better ideas. Heck, mine rusted away too. I just replaced it with new hose and said to heck with the pipe. That's asking for more grief down the road in my opinion. The hose is way less expensive too; I did mine for about $20 worth of hose, a Y-fitting and all new clamps.
 
#33 ·
I have the same issue with that damn water bypass manifold and of course, can't find one anywhere for my wife's 1994 Taurus Wagon. Any concerns on using hose right above the exhaust manifold? I'm thinking of cutting the Y adapter just into the hardline by the right fender to attach the hoses, then running hose across for the bypass and two for the heater core.

Anything special that I may have missed?
 
#25 ·
Well i just finished installing my "homemade" bypass because some of you told me to. It consists of two 5/8" tees and one 90 degree elbow. After all was said and done i took it for a spin hoping the problem was resolved. Unfortunately, my temp gauge is still laughing at me.

Im wondering if it is the fact that the bypass has such sharp bends because of the tees and elbow. It sure doesn't look anything like the original assembly which has nice smooth mandrel bends, kind of like an exhaust system. I don't think this could be the reason, but its very possible.
 
#26 ·
Let's use a little science here. If you have two engines in identical cars started at the same time will heat up at the same rate. They should unless three things are different 1) The heat input (gas flow) is not the same 2) heat loses are different(thermostat leaking to the radiator more or heater fan on) and 3) efficiency of the engines are different.

It takes a fixed amount of time to heat 500 pounds of steel(engine and transmission) and the only logical way to increase the heat up time is load the engine or reduce all heat transfer during warm up from the heater core or radiator. Shut the heater fan off and make sure the thermostat is sealing tight during warm up.
 
#27 ·
I guess its the title of the thread thats deceiving people. Sorry lol, you must be under the impression that the temp gauge is in fact rising slow. Well it isn't anymore after the plethora of components I have changed in the cooling system.

The problem now is that the coolant isn't staying within the range of 185-200. After about 10 minutes of driving, the gauge creeps down in a matter of 10 seconds to the point where the "normal" range starts. This temperature on my scanner registers to be around 160 degrees. The temperature will then slowly creep back up to around 195. On the highway the temperature will maintain the proper temperature. Once the driving turns into a stop and go situation, the temperatures start going crazy. Somethings obviously wrong if my temp is changing so fast.
 
#29 ·
Yes I have, it is a rt-1137 motorcraft thermostat rated at 197 degrees. Ive had it in and out a couple of times with suspicion that the thermostat was bad. I put it in a pot of boiling water and watched it perform like it is designed to. It was fully open at 197 degrees.
 
#30 ·
I had this issue with a 1975 Firebird that I installed a mechanical temperature guage that was so accurate it would show the thermostat cycling and could never figure it out. My guess and that is what it is is that your waterpump is not moving enough of water to keep the thermostat in a partially open range. I think the radiator may be batch cooling coolant instead of constant flow cooling. The elimination of the bypass could also cause the lack of blending. Pure guess ????
 
#31 ·
I think the radiator may be batch cooling coolant instead of constant flow cooling. The elimination of the bypass could also cause the lack of blending. Pure guess ????
Exactly. You could have a situation where the fan are running at idle (stoplight?) in response to a high block output temp caused by low flow. This "batch cools" all the coolant in the radiator quite a bit. When the car starts moving again, the pump starts moving enough coolant again, but it sucks in all the cold coolant from the radiator (a cold slug). The cold coolant runs through the block and causes the output temp to drop rapidly before the thermostat can react. Once the car has been driving a while the radiator coolant temp warms up and stabilizes as does the block temp once you've reestablished a good flow. The lack of of a bypass loop would only amplify the batch cooling effect since it would eliminate even more mixing.

So man up and take that water pump off like we've all been telling you do!!!
 
#32 ·
I guess i havent quite learned the trick to proper forum posting :p. I remember saying in one of my posts that I had changed a plethora of components in the cooling system. This does include the water punp. The old punp still had fins on it, but it was nowhere near like the new one. The only components that havent been changed is the radiator, upper and lower hoses, and the engine block if you want to count the water jackets inside. Everything else is brand new.

Sorry, should of said that in the first post
 
#34 ·
Not quite picturing what you're describing (the '94 mess looks different from the '90 mess even though they do the same thing) but as long as you route/support/tie off the hoses away from excess heat and motion near sheet metal you should be good.

My setup has two outlets from the block - one going to the heater core, one returning to the coolant pump - routed together by the Y-fitting just in front of the coolant pump which reconnects the return line with the heater-core return line. If it were electricity instead of liquid, it would be circuits in parallel instead of series. The most important thing to avoid is routing all of the coolant return flow through the heater core; if the core has any blockage at all, the engine cooling is compromised.
 
#35 ·
I agree on the"mess" statement. The diagram attached should shed some light on my issue and the Y pipe and sounds exactly like what you are describing. Two outlets from near the thermostat; one directly from the block that returns to the water pump through the Y connection and the other from the thermostat to the heater core. Then from the heater core through the Y and to the water pump.

I have kept up on maintaining the cooling system with flushes and fills annually. But now after 19 years, I have had to replace the freeze plugs on both sides of the block within the past six months and now this manifold (for lack of a better term).

But with the multiple metals used in the cooling system, I doubt you could ever keep from having any rust.
 

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#36 ·
Funny thing is, once you've removed every bit of it and rebuild the system with just hoses and clamps it doesn't look anywhere near as formidable. Do yourself a favor - when re-building, get rid of the metal Y-pipe and go with PVC or nylon instead. They're dirt cheap, and you eliminate the need to open the system again later.
 
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