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Topic: Thermostat and Thermostat housing (Read 3530 times) previous topic - next topic

Thermostat and Thermostat housing

I replaced my thermostat a few months ago and never had any problems till the last few days. It will overheat Almost all the way to the Hot mark then shoot right back down to the middle mark at random times. Sometimes I can drive and it will not do it at all. Well my question is when I was reading the manual it says the thermostat should "lock" into a recess on the housing by turning it a bit. On mine there was absolutely nothing to lock the thermostat into. Is it possible that it's bouncing around a bit causing my cooling system to go crazy? Has anyone else changed there thermostat and actually had it lock in? Thanks!

Thermostat and Thermostat housing

Reply #1 –
Might need to bleed your cooling system for possible air pockets. Make sure your coolant is proplery mixed and have your overflow bottle filled to at least the cold mark as well. It's a pain getting all the air out.
'98 Explorer 5.0
'20 Malibu (I know, Chevy, but, 35MPG. Let's go brandon, eh)

Thermostat and Thermostat housing

Reply #2 –
Test it in a pot of boiling water

Thermostat and Thermostat housing

Reply #3 –
Quote from: ThunderbirdSport302;405718
Might need to bleed your cooling system for possible air pockets. Make sure your coolant is proplery mixed and have your overflow bottle filled to at least the cold mark as well. It's a pain getting all the air out.
I bought premixed coolant so I'm sure that's good. The overflow bottle is just over the cold mark. I tried getting the air out the best I could. I left it running for about 20-30 mins with the cap off. Doesn't seem like it's moving much though. It dropped down once and I added more fluid. After doing that I couldn't get anymore air to the top.

Thermostat and Thermostat housing

Reply #4 –
Quote from: STANG8U;405720
Test it in a pot of boiling water

That was the first thing I did since I've had trouble with getting brand new thermostat that are bad.

Thermostat and Thermostat housing

Reply #5 –
Kinda off subject be does anyone know why this thread I started isn't showing up under "Find all threads started" on my profile page?

Thermostat and Thermostat housing

Reply #6 –
3.8,5.0? Waterpump bad? Radiator clogged?

If you look into the radiator while someone gives the gas a quick stab, what does the level do? Any swirling, gurgling, or odd stuff?
'98 Explorer 5.0
'20 Malibu (I know, Chevy, but, 35MPG. Let's go brandon, eh)

Thermostat and Thermostat housing

Reply #7 –
Quote from: ThunderbirdSport302;405733
3.8,5.0? Waterpump bad? Radiator clogged?

If you look into the radiator while someone gives the gas a quick stab, what does the level do? Any swirling, gurgling, or odd stuff?

Sorry I should have posted this to start with. It's a 88 5.0. When I changed the thermostat I drained the system and ran some cleaner through it. So I wouldn't think it would be clogged. What I drained to start with was clean and even with the cleaner I didn't notice anything in the anti-freeze.
I didn't have anyone around so I pressed on the throttle with my hand while I looked at it and I didn't notice any reaction inside the radiator.
As far as if the water pump is bad, Im not sure. How can you really tell? I don't hear any noise from the pump itself and there is no fluid leaking from around it. The only two signs I know of a failing water pump besides a steam ball exploding from it, haha.

Thermostat and Thermostat housing

Reply #8 –
I was thinking that if your coolant was low (due to a possible air pocket) that after the engine was hot, revving the engine with the cap off might show a little drop in fluid...sure sign that your w/p is moving fluid.

Maybe a bad connection on the temp gauge sensor/sender?
'98 Explorer 5.0
'20 Malibu (I know, Chevy, but, 35MPG. Let's go brandon, eh)

Thermostat and Thermostat housing

Reply #9 –
Replaced Temp gauge sensor/sender (both).  I'm thinking (hoping since I've never done a water pump....yet) it might just be some air pockets that are being stubborn.
If I let it run for a loooooong time with the cap off the level will drop a little, but barely noticeable and revving the engine seems to have no effect.
I even ran it had around the blocks for a bout 15-20 trying to heat it up really quick and the needle bounce upped pretty high while I that then dropped to middle. By time I got home and parked the needle was a little less than half and I was able to take the cap right off with out steam or fluid shooting off. And if I didnt just put a new cap on it I would say it's the cap, but I also eliminated that thought.

Thermostat and Thermostat housing

Reply #10 –
Also I took the cluster out earlier and took a reading from the R/W wire from the temp sending unit to behind the dash and only got .7 OHMS so I'm thinking the wiring is fine.

Thermostat and Thermostat housing

Reply #11 –
Also I was really hoping someone could answer my other question. About if the thermostat is really supposed to "lock" in the thermostat housing. Or do you just place it in there with the gasket and just bolt it on. I've read three different books for my car they all say the thermostat is supposed to be twisted into the housing. but my housing is smooth and has no groove for it lock into.

Thermostat and Thermostat housing

Reply #12 –
Far as I know the t-stat drops in, then the neck goes on and bolts it down tight.

My gut is either an air pocket or possibly even the w/p's impeller fins are corroded to the point there's not much if any flow. This happened to my 92 5.0 truck...the summer of '02 I noticed it gradually getting hotter. Ended up being the pump, of course, the collateral damage of twisting off a couple of the bolts sucked a fat one. I took it to the shop since I didn't have the means to get the bolts out, they dropped the pan, messed up the pan gasket, and finished it off by tossing in a new timing set.

Truck had a severe lack of maintenance when I bought it, after I fixed a lot of little piddly stuff, it was great runner. Ran the day I sped it. I will always kick myself in the ass for that.

Sorry for the tangent here...lol,
'98 Explorer 5.0
'20 Malibu (I know, Chevy, but, 35MPG. Let's go brandon, eh)

Thermostat and Thermostat housing

Reply #13 –
Quote from: ThunderbirdSport302;405761
Far as I know the t-stat drops in, then the neck goes on and bolts it down tight.

My gut is either an air pocket or possibly even the w/p's impeller fins are corroded to the point there's not much if any flow. This happened to my 92 5.0 truck...the summer of '02 I noticed it gradually getting hotter. Ended up being the pump, of course, the collateral damage of twisting off a couple of the bolts sucked a fat one. I took it to the shop since I didn't have the means to get the bolts out, they dropped the pan, messed up the pan gasket, and finished it off by tossing in a new timing set.

Truck had a severe lack of maintenance when I bought it, after I fixed a lot of little piddly stuff, it was great runner. Ran the day I sped it. I will always kick myself in the ass for that.

Sorry for the tangent here...lol,


See that's my issue with "dropping in the thermostat." Alot of cars I've worked on you just drop the thermostat down, but on these cars the hole is vertical and little tricky to get to so I worry it's not sitting right. I'll try to get any air out the system again tomorrow. I'm really hoping it's not the water pump, but my girlfriend loads me up with any tool you can name for Christmas so I think I can manage it. I just might freeze my but off before I'm done. But is there no real sign of a worn down water pump cept it getting hot?
No worries about the tangent, lol. I'm sure we all have some stories about our histories with our cars.

Thermostat and Thermostat housing

Reply #14 –
Water pumps are not that bad to replace on these cars.  The thermostat, as long as the spring side goes into the intake manifold side, it should work just fine.  They can be a little finicky to seal, I use the felpro paper gasket coated nicely with Permatex Indian-head shelac, then tighten the bolts. 

For the water pump, you can use the Permatex shelac or rtv sealant (blue or black) lightly coated onto the pump to plate gasket and then the plate to timing cover gasket.  Just be very careful when removing the water pump bolts.  Some of them go into water jackets and get corroded and snap easily(like Thundersport302 said)

Make sure to get the correct pump ( the Panther chassis looks similar but rotation is different) and use the gaskets in the Felpro kit that match what was on your old waterpump.  I use the Felpro over whatever gaskets may come with the waterpump.

If anything this would be a good preventive maintenence before the summer months.  Good luck!