5.0L thermostat install question

[ford99_1979]

I have performed a search and I see discussion and threads about the 4.0L thermostat but could not find anything on the 5.0L thermostat directly. I have had a leak for a long time and finally got around to removing my thermostat housing. I see a combination of paper gasket and silicon sealant. I cleaned up my thermostat housing with a dremel and wire wheel and noticed it does not have a good sealing surface on the cast thermostat housing. I don't have good faith that this sealing surface and the paper gasket are going to do the job and I hate to have to do this again really soon.

My question is what do you guys do for a good and permanent seal?

Here is the questionable sealing surface.

 

[koda2000]

you could replace the housing, or you can true it up with a file and sandpaper. put the sandpaper on a flat surface and rub the housing over it on one direction until the surface is flat. changing directions makes it easy to see how you're doing. if it's not a flat surface, it will leak and no sealant will be able to stop it because of the water pressure in the cooling system. I would true it and put a light coating of silicon sealant on it before reinstalling.

tip: put the thermostat in the housing and glue the gasket on the housing and let it sit overnight (or at least a few hours) this makes it much easier to reinstall the housing w/out the gasket or thermostat moving around. I've also noticed that the jiggler valve only wants to face in one direction because the housing had a slight relief for it.

 

[ford99_1979]

Thanks for the advice koda. I will definitely try to true up the surface. I see a few of these housings on ebay that are in way worse shape than mine for too much money.

So would you use hi temp sealant or the paper gasket?

 

[koda2000]

Thanks for the advice koda. I will definitely try to true up the surface. I see a few of these housings on ebay that are in way worse shape than mine for too much money.

So would you use hi temp sealant or the paper gasket?

you don't need hi-temp sealant for cooling system gaskets. I like to smear a little clear silicon on both sides of the gasket to waterproof it (as most are paper). if you look in the auto parts store you'll see several different types of sealant for different jobs:

clear silicon (okay for some things, but can harm some sensors)
blue specifically recommended for cooling system (but I don't like it)
copper for hi-temp (like exhaust)
black for oil pan and valve covers
red (not sure what it's specified for, but my personal favorite for almost everything).

while your at it, you should replace that small bypass hose. looks pretty shot.

 

[ford99_1979]

you don't need hi-temp sealant for cooling system gaskets. I like to smear a little clear silicon on both sides of the gasket to waterproof it (as most are paper). if you look in the auto parts store you'll see several different types of sealant for different jobs:

clear silicon (okay for some things, but can harm some sensors)
blue specifically recommended for cooling system (but I don't like it)
copper for hi-temp (like exhaust)
black for oil pan and valve covers
red (not sure what it's specified for, but my personal favorite for almost everything).

while your at it, you should replace that small bypass hose. looks pretty shot.

Ok surfaced the housing

I also got some red silicon. This morning I did pick up a new bypass hose as NAPA had one in stock!! So i'm ready to rock. Thanks again for the advice. Its a simple part, but I know certain proper steps need to be taken to avoid premature failure.

 

[koda2000]

looks good from here.

 

[Joe Dirt]

I just re-sealed my water pump with the Permatex thermostat/water pump gasket silver sealant. Worked better than the blue previously, I never cared for blue.

 

[SoNic67]

+1 - that's what I used on mine too.

 

[ford99_1979]

the auto parts store I went to did not have the waterpump & thermostat stuff. After I surfaced the thermostat housing I ended up just using the paper gasket. The paper gasket I got cam with adhesive backing on one side which holds the thermostat in place while installing. With 2 good mating surfaces and a proper gasket I feel comfortable with the install. Good to know there are options though. If It doesn't work I will be going to that waterpump/thermostat gasket stuff.

 

[TekMan05]

Hey guys, I know I'm resurrecting the thread here. But I've been suffering poor MPG's lately as it's gotten colder. I remember last year I replaced my thermostat with a 160* one instead of the normal temp. Would this have a negative affect on fuel economy? If so I'm thinking of swapping it out if that's the case. Thanks!

 

[koda2000]

the coolant has to reach full operating temp in order for the ECU to allow "closed loop operation". if the coolant temp is insufficient for this to happen, you fuel economy will suck. it's like driving with the choke on all the time. your engine and ECU were designed to operate with a 192-195F degree thermostat. i suggest that you change out the 160F t-stat.

 

[TekMan05]

Hey thanks, I was beginning to wonder considering the temp gage only makes it about a third of the way across instead of half. I think at the time a year ago I figured a cooler engine would be a better running engine. Why would they have a 160 degree thermostat for our trucks in the first place?

 

[pbnj22]

also "winter blend" gas takes its toll on gas mileage too.. and all that slush and snow on the road tends to hurt rolling resistance thus lower miliege.. but yeah your bigger problem would be thermostat.. a lower degree t stat will cause a rich condition, and mess with your spark and timing, hurting gas mileage..

 

[TekMan05]

Figured so that and my truck is cammed as well. I swapped it out last night and the guage definitely went up a little bit more than before. Still not Perfectly in the middle where the little graphic is but past the one third mark from before. After inspecting the old one it was actually a 180* not 160*. But now has a OEM set 192* now. Too soon to report Fuel economy. We got a slight dusting but no real snow fall so far.

 

[koda2000]

Hey thanks, I was beginning to wonder considering the temp gage only makes it about a third of the way across instead of half. I think at the time a year ago I figured a cooler engine would be a better running engine. Why would they have a 160 degree thermostat for our trucks in the first place?

they don't make a 160F degree t-stat for our trucks. they make a 160F degree t-stat that happens to fit our engines. that doesn't mean it's recommended you use one.

you you're still getting poorer than normal fuel mileage, you might consider replacing your up-stream O2 sensors. these effect fuel trim levels and when they wear out they can adversely effect fuel economy. heated O2 sensors are good for aroun 120K, unheated around 60k. i'm not sure which a '96 would have. you can tell by the number of wires on them. 4-wire = heated, 2-wire = unheated. a bad ECT sensor can also mess with your fuel economy.

 

[Steeda04SVT]

they don't make a 160F degree t-stat for our trucks. they make a 160F degree t-stat that happens to fit our engines. that doesn't mean it's recommended you use one.

you you're still getting poorer than normal fuel mileage, you might consider replacing your up-stream O2 sensors. these effect fuel trim levels and when they wear out they can adversely effect fuel economy. heated O2 sensors are good for aroun 120K, unheated around 60k. i'm not sure which a '96 would have. you can tell by the number of wires on them. 4-wire = heated, 2-wire = unheated. a bad ECT sensor can also mess with your fuel economy.

Great info, thanks for posting that. On my temp gauge it's barely reading into the normal range since I bought in the middle of this summer. So hoping mine goes smooth as well and am going to get a motorcraft t-stat for mine along with that sealant you guys recommend. Thanks for the info.

 

[Blk2kXLT]

Ok surfaced the housing

Wow thanks for the suggestion. I have been fighting my housing for 2 gaskets already. I grabbed a file and cleaned it nice and flat and also took a wire wheel to the block mount area. I think this will work out now.
I took suggestions from another thread to use the grey (water fitting) RTV to "glue the thermostat into the housing and then thin layer with gasket also and let dry before attempting. (Also have the air vent in thermo facing up)