Odd Cooling System Phenomenon

[ERUSH97XLT]

Hello,

I have a strange event with my cooling system:

I just replaced the water pump and thermostat. After doing so, I flushed the cooling system and refilled with fresh coolant as well as burped the system.

So, here's the odd part: my temperature gauge fluctuates with a predicatable frequency (it's not random). The instant I attain normal operating temperature, my gauge drops way down to cool, then warms up again slowly. In essence, it "warms up", then "cools down" in about three seconds, then "warms up" again in about ten seconds.

I got freaked out the first time this happened, so I stopped the car when the gauge read cool, opened the hood, and my upper radiator hose was pinched shut!! I opened the radiator cap to release the vacuum and filled the radiator. This keeps happening; whenever I park, I wait for the gauge to drop to cool, then release the vacuum and refill with coolant. Each time this happens, I use less and less coolant to fil the radiator. Another odd part: the radiator isn't drawing coolant from the reservoir.

Any thoughts as to what the *%^&#*$( is going on? Should the radiator cap be replaced? I hope I don't blow a hose while driving due to the intense vacuum. . .

I should also note that I installed the thermostat in the correct orientation, and it does not have a air hole (neither did the stock one).

Thanks for the help,

ERUSH

 

[Vargas]

Probably a bad cap. A good cap will not allow system pressure to be lower than atmospheric. When that pressure differential exists, a properly working system will draw coolant from the expansion reservoir. The only other thing you might check is to verify that the hose to the expansion tank is not blocked.

 

[ERUSH97XLT]

Thanks for the reply,

I know for a fact the reservoir hose is not blocked; I verified this a few days ago by draining the coolant from the reservoir through the hose.

I will purchase a new cap from Motorcraft. They're relatively cheap and hopefully I will notice improvement immediately.

Thanks,

ERUSH

 

[Vargas]

I guess there could be a blockage at the radiator neck where the tank hose connects, but if coolant level rises in expansion tank when engine warms up then you know it is clear.

About the only thing it could be is a faulty cap. At least they are fairly cheap, as parts go.

 

[ERUSH97XLT]

So I just replaced the cap with a Motorcraft replacement. I haven't seen any results yet, but I'll keep checking my reservoir and ensuring the upper hose doesn't collapse.

I also ensured there weren't any blockages in the stem for the reservoir hose at the radiator filler neck.

We'll see what happens. . .

ERUSH

 

[ERUSH97XLT]

Ok.

So I've driven for a while with the new Radiator cap. No improvements, though the collapsed upper hose issue has been solved. The gauge still cycles with a predicatable frequency. I have noticed that the fluctuations are not as intense as before.

I have another thought: Ford has issued a TSB a while back pertaining to water pumps not providing adequate flow which can cause temperature gauge fluctuation. I just replaced the water pump with an new ASC pump. Ford recommends their "improved" design to correct this flow problem. Could the pump that I purchased be of the old, inadequate design? Should I by a Motorcraft one? Has anyone had any problem like this in the past with aftermarket pumps?

Thanks,

ERUSH

 

[Vargas]

Let me make sure I understand the symptom fully.

It only happens once, as soon as the gauge reads normal operating temperature?

The cap fixed the vacuum/pinched hose issue. Does the radiator give/take from the expansion tank now?

If yes to both questions, it has to be either be air trapped in the system, or a sticky thermostat. Thermostats are cheap. Get the air out, buy another thermostat, and drill a weep hole in the thermostat before installing it.

 

[ERUSH97XLT]

After I replaced the cap, the symptoms are the following (I'll be as specific and articulate as possible):

The temperature fluctuation happens more than once while I'm driving with predictable frequency. As soon as the gauge gets to the usual operating temperature spot, it remains there for about 30 seconds. After this short period, the gauge drops outside the normal range (touches the 'C') within a 2 second period. It remains "cold" for about 15 seconds, then climbs back up to normal operating temperature, and the cycle repeats with similar frequency. I say "similar frequency" because I haven't timed it with a stop watch: I roughly counted the time interval between the gauge activities. Would an air bubble behave with predictable frequency? I'm not certain...

I have not witnessed the collapsed hose issue since replacing the radiator cap, so I think it's safe to assume this issue has been resolved. Coolant is being exchanged from the radiator and reservoir (as witnessed in the varying amounts of coolant in the reservoir).

Ok. I hope this helps alleviate some confusion.

Here's another wrench in the works: This periodic oscillation of my temperature gauge does not occur when my truck is idling in my driveway. I literally sat in my car for a half hour and watched the needle. It was steady as ever. . .

I will try something else to help narrow this down: since it's been rather cold, perhaps this issue is related to the heater core (i.e., blockage, heater control valve, etc.). I will drive with the climate control knob on "full cool" to see if this fluctuation is affected. What do you think? If the needle stays steady while the knob is on "full cool", I know something is happening beyond the heater control valve (including the heater control valve).

Thoughts?

ERUSH

 

[96eb96]

The OHV engines seem to fluctuate, mine does too but somewhat less than yours. There is some theory about steam formation in the system and there is a bypass kit that may help (I don't have it though) What brand stat did you use? Also, the one wire coolant sender may be too sensitive, when I replaced mine it seemed to help a bit.

OHV engines have the bypass cast into the intake (there is no internal hose). From what I understand that is part of the issue.

 

[Vargas]

Thoughts?

ERUSH

Does this cycle happen in stop&go driving as well as extended steady speed (aka freeway) driving?

 

[ERUSH97XLT]

Does this cycle happen in stop&go driving as well as extended steady speed (aka freeway) driving?

Yes. It occurs in all conditions (stop/go and freeway) except when idling casually in my driveway.

ERUSH

 

[Vargas]

How's the fan clutch?

 

[ERUSH97XLT]

How's the fan clutch?

Excellent question: I'll investigate tomorrow. It took A LOT of muscle from myself and a friend to get the fan off when I replaced the water pump; perhaps I damaged it.

 

[ERUSH97XLT]

*sigh*

Here's a new symptom:

I get this thumping noise from the passenger side while idling at operating temperature.

There are two TSBs that adress this issue. Ford claims the following in each:

1. The water pump may be causing uneven flow, thus causing steam to form and creating the thumping noise.
2. This could be caused by a number of things causing a local overheating condition (thus the steam and thumping). This could be caused by either of the following (1) exhaust restriction; (2) cooling system restrictions (i.e., kinks, clogs, etc.); (3) incorrect coolant-water mixture; and (4) coolant leaks.

I highly doubt my water pump is causing uneven flow; it's brand new. I could have an exhaust restriction, but I haven't noticed any decrease in mileage or power that would support this. I know for certain I don't have any coolant leaks because my reservoir hasn't shown any indication of coolant loss (yes, I'm properly exchanging coolant now since my cap fix). I'm thinking I have a clog or restriction somewhere (heater core area, heater control valve?).

I should stress that I really didn't perform a formal coolant flush. I simply drained the radiator and block. I didn't use a flush kit due to the cold temperatures. Further, I did my best to clean out the water pump mounting cavity from gasket scrapings, but is there a slight chance a piece of old gasket is stuck somewhere?

I'm planning on taking a road trip in a few days. Will my car blow up if I don't fix this immediately? I just don't want to blow a hose or spring a leak because something is out of whack.

I should also stress that my gauge doesn't indicate that I'm overheating. And I've noticed today that my gauge fluctuates while idling in my driveway. This tells me something is getting worse.

Any thoughts? Is there any danger if I take this vehicle on a road trip?

ERUSH

 

[Vargas]

I don't suppose you have or have access to an IR noncontact thermometer? There are two things I'd check. Is there a temperature difference between the left and right sides, and is the fluctuation of the gauge representative of an actual temperature change?

 

[ERUSH97XLT]

I don't suppose you have or have access to an IR noncontact thermometer? There are two things I'd check. Is there a temperature difference between the left and right sides, and is the fluctuation of the gauge representative of an actual temperature change?

Nope. I have no idea if the temperature fluctuation represents actual temperature information. This is what scares me. I don't want to blow up when on my road trip. . .

Thanks for the reply.

ERUSH

 

[jremington59]

You could have air in your system. You need to park the vehicle with the nose up, remove the cap and idle it and burp the air out of it. Let the radiator go down a couple inches and just let her idle. When you see it drop down, add a little more. It can take a while to get all the air out of there. Make sure to let the radiator go down a ways or it will slop everywhere.

It should vent back through the overflow tank but sometimes they don't. Pull the rubber line off the radiator spout and blow through it and make sure the rez opening isn't plugged.

You're sure the thrmostat is good?

 

[ERUSH97XLT]

Ok.

I just tried burping the system. It slopped and blooped and regurgitated fluid for a little while... so I stopped the car and refilled the radiator. We'll see what happens on the way to work tomorrow.

One thing happened that was cause for alarm:

When this thing was burping, the engine was popping (like popcorn), like it does when it overheats. This stopped after about a thirty seconds. Could this be anything significant?

ERUSH

EDIT: I'm fairly certain the thermostat is ok; I just replaced it. What are the chances of getting a bad one out of the box? It's a stant.

EDIT 2: Maybe that popping was moving air through the system...? I know for a fact that popping sound is not good, but since it stopped, I'm ok??

 

[Vargas]

I think the popping is just steam flashing due to no pressure with cap off.

 

[ERUSH97XLT]

Ok.

This sucks! It never did this before and is really annoying!

Here is what I'm going to do based on all your fine input:

I'm going to jack front end up (my driveway is flat) and burp through the service port (the highest point) behind the heater control valve. The thought behind this is to force air out of the heater core. My dad has done this technique for years with 100% success. If this fails, I'm going to pull the thermostat and do a bench test with boiling water. If it passes, then I'm going to drill a hole at the 12 o'clock position, reinstall, and re burp through the service port. This should eliminate all air pockets. Period. Then we can discuss other sources of air or assymetrical heating (combustion gas infiltration, clogs, etc.).

What do you all think? After searching the internet for hours last night, I'm pretty confident I have air trapped somewhere (thank you jremington59 for the tip!). In my opinion, this is the easiest procedure to perform (compared to removing head, etc.).

Thoughts?

ERUSH