cooling circuit

[ckinart]

hey everybody... i've got a quick question, but first, some background info:
i have noticed the past few days that whenever i go anywhere in my SHO, the temp. gauge climbs slowly for the first few minutes (as usual), then climbs rather quickly to the "N" in "NORMAL", stays there for about 30 seconds, and then drops very quickly to where it should be (in my opinion)... thing is, this morning was the first time i had the heat on when this happened, and i noticed that i didn't have any heat until the temp. dropped from the "N"... this may be a simple sticking thermostat, but my concern lies in the heater core... is the heater core part of the primary cooling circuit? i.e. if it were clogged up, would it cause the core engine temp. to rise like this? if not, it doesn't make sense to me that it would be the t-stat sticking... if it were stuck closed (making the temp. rise so much), i should still have heat, right?

if it matters, i replaced the t-stat and the temp. sending unit last year.

anyway, what do you think?

<small>[ September 24, 2002, 09:44 AM: Message edited by: ckinart ]</small>

 

[BeatDaSHO]

ur lucky man. my engine heats up and stays at the N and won't come down. Looks like you might have a bad temperature sending unit. About 6 bucks at any auto store. Easy to fix. You also might have a sticking thermostat so go ahead and buy the motorcraft thermostat. i believe the 180 cannot be found anymore so go with the 192 degree.

Greg

 

[sdpatt]

The heater core's only purpose is to provide heated coolant for warming of the climate control air. It has no function dealing with cooling of the engine. It sounds like a sticking thermostat is your problem and you should search for the 180 degree Motorcraft thermostat.

 

[ckinart]

scott: thanx for the input... next question:
if the t-stat is sticking, that would adequately explain the temp. spike which would drop off once the t-stat "unsticks" due to the overtemp... however, because the heater core gets its heat from coolant circulated independently through the engine, then why would i get no heat in the cabin until the temp. spike dropped off?

i must be misunderstanding something...

and does it seem unusual that, despite replacing the t-stat last year, it would be sticking already?

<small>[ September 24, 2002, 02:22 PM: Message edited by: ckinart ]</small>

 

[Red One]

You've got air in the cooling system. When the t-stat is closed the air is trapped in the heater core so you get no heat. When the t-stat opens and the coolant will flashed to steam (the spike) and then some of the air is purged and you get heat from the heater core.

Air in the cooling system is 99% of the t-stat and sender problems with the V6. The extreams created by the steam flash will distort the t-stat and change the spring tension. It will also affect the sender's calibration.

 

[ckinart]

thanx red one... i read another post explaining how to get the air out of the system (remove rad cap, allow engine to heat up, right?), but this begs the question: how did air get in the system?

 

[Red One]

poor engine cooling design.

If you remove the coolant hose gong to the IAC when you fill it will allow most of the air to get out. make sure the pressure cap is good too and the overflow tank stays full.

 

[Aspect]

It could be air but with a sticking T-stat, you would see those exact symptoms. The temperature reading is taken before the water goes through the t-stat back into the radiator. The t-stat acts as a plug to slow the water going thru the coolant system to decrease warm up time and to maintain an even temperature across a wide band of operating temperatures.

During start up where your needle goes to N, the t-stat is in its closed state. The coolant is not flowing adequately enough so the coolant inside the motor is getting to very high temps, but the temp of the radiator coolant is still very cool in comparison. Once the temp raises high enough for the coil to start functioning properly, it opens, coolant flows, and that's when you see the temp drop from the N.

Now the reason you have no heat is that the T fitting that diverts water to the heater core is before the water enters the motor. Since it is pulling cool water from the radiator it would cooler until the T-stat opens, allowing the hot coolant to heat up the cooler coolant to give you hot coolant in your heater core.

The reason I don't think it is an "air pocket" is that usually the sign of that is when you spike for no apparent reason after the motor is at operating temperatures and not usually at start up.

<small>[ September 25, 2002, 02:52 PM: Message edited by: Aspect ]</small>

 

[ckinart]

thanx aspect, i understand exactly what you're saying... i suspected precisely what you have described, but i had thought that the coolant to the heater core ran in a circuit direct from the core engine, which would mean if the engine were hot (due to a sticking t-stat), i should have heat in the cabin... evidently i thought wrong... if the heater core gets coolant from a tee fitting that leaves the primary cooling circuit before entering the engine, then the rest makes total sense...

interesting thing is, based on earlier advice, i ran the engine with the rad cap off for a bit, and a bunch of air gurgled up out of the rad... (i haven't taken the SHO out since to see if the issue is gone)... oh well, if that didn't do it, i'll replace the t-stat... not a problem...

thanx very much for your help everbody. thumbs_u

 

[rangerj]

CK,

Where did the air in the system come from? Did you have the system open, say to change a hose, and not get all the air out, before putting on the radiator cap?

If this is not the case, you may want to check for a poor hose connection that could be sucking in air. Check the hose at the overflow bottle, by the radiator cap, first. If you have not replaced the radiator cap in several years, or if you do not know how old it is, replace it.

If the problem persists you should pressure test you cooling system. If this does not find the solution, then consider getting a chemical "test kit" to test for exaust gas in the coolant. (Available at auto parts stores)

After you replace the thermostat, you can minimize the amount of air in the system by removing one end of the small hose under the throttle body. When coolant gets to that point, reconnect the hose. This is a "high" point on the engine, and will allow most of the air to escape while you slowly fill the system.

Start the engine with the heat on maximum, so that the heater core is open to fluid. Do not put the radiator cap on until you have watched the coolant turn over three or four times, that is the thermostat has opened and closed several times. This should get the air out of the system.

Put the thermostat on, completely, before you shut down the engine, or you will have hot cooland gushing out of the radiator.

Keep you eye on the temperature while you are doing this, and do not let the temperature get into the "red". It should not get much past the "R" during this process.

The little "jiggle" valve on the thermostat is there to let air get through the thermostat. That is why you put the valve on top when you install the thermostat.

If your problem is not fixed after you replace the thermostat and radiator cap, and have checked your hose connections, then you should check for exaust gas in the coolant.

Gee, I got through all that without once telling anybody to search the archives. Hope this helps. rangerj

 

[rangerj]

Correction to my last post:
It should read, "put the RADIATOR cap on completely before shutting down the engine......"
Sorry! rangerj

 

[ckinart]

thanx for the post ranger...
i actually think i got the problem licked... i was searching some of the other posts on this subject, and found that the first thing most people mentioned was low coolant... i thought i had plenty of coolant since the recovery tank was full as always, but decided to add coolant anyway to see how much it took... well, it took alot... i gurgled all the air out of the system (i recently changed the upper rad hose, which is probably where the air came from in the first place), and the temp. works exactly like it should now... problem solved thumbs_u

then i got to wondering why, when i changed the upper rad hose, the coolant that was lost during that job wasn't simply recovered from the "recovery" tank... i took the tank out, and poured it out, and found that there was about 3 inches of sludge in the bottom eek!
i guess this car had been a little neglected before i got it... i cleaned out all the "foreign material" (it may have been some of that "leak stop" stuff) and made sure that the recovery hoses were all clear, and put it back together... i'm having the entire system flushed as i type, and i think i'll be back to 100%... (and i'm aware of the risk of springing a leak after a flush, but i'd rather do that and fix the leak(s) than force a heater core replacement due to a dirty system)

sorry for the long story, but i like to follow up my posts with the results of my troubleshooting for others to search through later... especially my successes thumbs_u

thanx again all...

<small>[ September 28, 2002, 01:24 PM: Message edited by: ckinart ]</small>

 

[93MTXSHO]

Hey I have one question. My 93 always has a little bit of "sludge" in the bottom of the overflow tank. I've always wondered about it, and since it was brought up I thought I'd ask if anyone knows where it comes from. About every 6 months or so I just dump out the bottle and wash it out. Just wondering.

 

[SHOZ123]

Sludge is from air in the system. It is rust.