1991 F350, 7.3 IDI, 5-speed manual transmission, air, withBanks Sidewinder wastegated turbo.
My truck’s coolant system appeared to be running fine – no overheats,no leaks or drips. I just happened to discover that the shop that had performedmy last coolant flush and change seemed to have really screwed it up - noremoval of block drains, incorrect coolant and incorrect amount of SCAs. Sodecided to do it myself. I’ve read every thread I could find on coolant,cavitation, etc. and (wouldn’t you know it) I still have managed to come upwith a couple of new questions. I’m stuck in limbo waiting to proceed so justhad to try to resolve these issues before going on. My wife thinks I’mobsessive . . . I like to think I am just thorough . . . .

• Where’sthe coolant? I jacked up the front end, drained the radiator using the drainplug and disconnecting the lower hose, removing both block drains,disconnecting the heater hoses and drained the heater core by blowing throughthe lines, then lowering the front end to make sure no coolant pockets were trapped. . . total amount of coolant recovered. . 5 gallons!
• Tookyour guys’ advice and changed the thermostat. Wouldn’t you know it – it had aChinese version (88C)! Truck seemed to be cooling properly so why with an 88Cwhen the Ford OEM 8575 is 97C. Should I be using a different OEM stat becauseof the A/C?
• Ihave read where some of you recommend adding some coolant through the heaterhoses. I assume this is to put some coolant into the dry block after fully drainingby removing the block plugs, right?
• Finally,what is the consensus on using gasket sealant on the thermostat gasket? I’veonly found two references one for and one against.

Sorry for the long post but . . . I am just trying to be “thorough.”As always thanks to the experts that make this forum THE BEST!

 

i can never seem to get it all out .. 5 gallons is pretty good actually ..

if you want it all fresh you have to plug it back up and run distilled water through it ..

flush .. repeat .. a few times .. to get it all .. some just stays up in there .. where ? it's a mystery ~

i don't know but i used a dealership motorcraft one .. looking back i wish i had gone one step hotter .. now my motor runs too cool all the time .. but .. hey .. it's alright .. next time i'll go one step hotter .. i don't even remember what one i put in there ..

i have added coolant into the heater hose to get past vapor lock when my coolant wouldn't 'take' though .. it seems few others have had this problem .. so maybe mine was just a rarity .. i couldn't get more in then enough to fill the rad till i put a funnel on the heater hose and primed it ..

i would seal the thermostat gasket .. just because it's cheap insurance as long as it's not a dry gasket location .. with mine i HAD to seal the gasket because one of my bolts broke and i had to carefully retap the block ..

so yea i used sealant and alot of it in hopes that i wouldn't have to get in there for awhile .. no problems .. it's dry and doesn't leak .. but i just wish i had gone one hotter ..

 

When you have the thermostat housing apart, get a motorcraft thermostat and then remove the little ball bearing inside the radiator hose connection/upper cast piece that the thermostat goes in.
It will make bleeding air from the system /so/ much easier, and doesn't really affect how quickly the system warms up.

 

i drain radiator, and reverse flush with garden hose. same with heater. then remove thermostat and run water through block till clean clear water comes out. then put it all back together and fill radiator with 2 1/2 gallons coolant and 2 quarts napakool. been doing it this way for 494,000 miles without any problems.

 

Okay . . . . time for me to go nuts! As mentioned above, replaced Chinese 88 degree thermostat with Ford OEM stat (8575-C). Now the temp gauge will not even make it to the N or Normal, even after 45 minutes of driving. In addition, the cold start/idle solenoid will not turn off allowing the idle and advance to go to a warm state. The needle will fluctuate slightly up and down but that's it.


The bypass in the thermostat is open and ball moves freely. I tested the thermostat before installing.


If anything, this problem sounds more like a thermostat stuck open rather than stuck closed.


Thoughts from the experts?


BTW thanks to others for previous responses.

 

When running at operating temp about 190-92 my trucks dummy gauge sits right at or right before the N on the word Normal. Like I said it is a dummy gauge and isn't all that accurate.

 

Mine is in the same range(I have a digital gauge too), and yes, it's usually right at that point.

I'm not going to say it's a dummy gauge, though - once it gets up to the L you know it's getting hot. And that's like 212-225 or something like that.

 

Yes mine is right around the same. I much rather prefer the aftermarket gauge over the stock one though any day worth the investment for sure