Hello. This thread will probably be similar to others and in addition to one I had started earlier, but I need a specific answer. I have an '89 F-150 crew, 5.0 302 manual 5speed. I am needing to replace the thermostat, but there seems to be a compatibility problem that I am not comfortable with until I hear from you guys. I bought a thermostat from O'Reilly's (part number 3009) manufactured by Murray. I finally got my old thermostat housing off and removed the thermostat and noticed that the one I bought and the one that I am removing looks different. On the old one, opposite the spring side, the ridge that fits into the housing is much larger. As it fits into the housing, the manual says to give it a slight twist clockwise as shown below.
Fig. 6: On gasoline engines, turn the thermostat CLOCKWISE to lock it into position on the flats in the outlet elbow


It fits snuggly into the housing. The new one doesn't have a ridge. It seems to be held into place by the tightening of the housing back onto the engine. My problem is that there is a lot of pressure that goes throught this system and if it malfunctions, then the truck will act rather retarded. I am concerned that the thermostat will not do as it is required. Here are some numbers that I found on the old thermostat E7UE-8575-A2A (Motorcraft). If there is another engine in which this type of thermostat will fit, I could probably use it. The gasket works, but the thermostat seems off. I would like to know because it will give me some insight on other parts that were put on this truck before I bought it. IF I had a digital camera, I could show pictures and give you a better idea of what I am refering too. Nonetheless, I hope someone can help me here.

 

That's odd. I've never seen a thermostat you need to twist and lock into the housing. Usually the housing has an indent that the thermostat sits in, keeping it away from the sealing surface of the housing and block. If the thermostat sits above the sealing surface too much and won't be held still by the housing bolted to the block then I wouldn't trust it either.

 

There is an indentation within the housing. This indentation makes the housing hole out of "round". This out of round indentation is what makes the thermostat able to be twisted within the housing to fit snugly before placing onto the engine. There is clearly a differnce in the two thermostats and I am sure that there is a thermostat that will fit, even if from a differnt make and model vehicle. I am going to take a picture so you will be able to see exactly what I am talking about. Please recheck this thread within the next few days.

 

Hey guys (and gals)! Sorry to get back with you so late on this issue. I finally got the camera. Anywho, to continue with this thread here are some pictures of the theromostats and housing that am having problems with. As you can see the old thermostat has a inside ridge and shape that gives it a snug fit. The new one has no ridge and fits loosely. Only by putting the gasket on the correct side will help to seal the thermostat in after bolting it down. Can someone tell me why the change in model and what other engine may have a similar theromostat? This may not even be a Ford engine that I have in this truck, but it looks like the others I have seen. Should this be a problem or will the gasket and bolting allow the thermostat to work just fine?

 

Eh, don't see a problem here as long as the outer diameter of the new t'stat sits securely in the recessed area of the housing. Don't know that the raised portion seen on the old stat makes a difference.

 

It doesn't matter, the new thermostat will work perfectly. There is no need to worry. The recess in the housing keeps the thermostat in the correct place and the fit of the thermostat in the housing doesn't have to be tight. The gasket will keep water from leaking out from between the housing and block, and if any water can pass by the thermostat internally when bolted together it doesn't matter.

The only thing I don't like about the new thermostat is that you bought the cheap one. Don't cheap out on the thermostat, buy the high performance one at the recommended opening temperature.

 

Great advise, but I want to make sure that I understand the comment by wde3477. The raised portion of the old thermostat is what sits INSIDE the housing. Because the hole is actually out of round, it can be turned clockwised and fit like a hand in a glove. No movement, even if turned upside down or dropped. The remainder of the thermostat seals the hole and the gasket is the icing on the cake. The new thermostat only COVERS the diameter of the hole, the gasket holds it in place and bolting it seals the deal. Nonetheless, I can understand that there shouldn't be a worry if it is installed correctly. Sean, what is the correct operating temperature of the thermostat and do they come based on that temperature? Also, what will a high performance thermostat do for a standard F150 engine? I didn't know that it mattered. Thanks.

 

I believe the recommended opening temperature is 190 degrees, but they can tell you at the parts store. You should always use the recommended temperature on fuel injected vehicles so the engine will come up to the proper operating temperature fastest and save fuel. The thermostats are available in a wide variety of opening temperatures, as cool as 160 degrees. The high performance thermostat is just better quality, and if there is a problem with it or the engine overheats then it is designed to stick open instead of sticking shut. This will save you from frying the engine.

 

Sounds good to me. I will replace with the higher performance, it is only a few bucks more. I assume that the the worry is still not an issue? Thanks

 

Believe you guys have this concern handled. Would like to make a comment about t-stats in general for other readers. Always the spring side of the t-stat is what measures the water temp. It has to be toward the engine not facing the radiator. The push and turn thing. Look at the old original ford t-stat, do you see the little brass rivet thing. I can see it in your pictures. That is a bleed hole to help purge air out of the system. The housing fits the manifold only one way, the push and turn thing makes sure that the bleed hole is on the upper half of the housing to help bleed the air out of the engine. It is not a requirement, just a ford thing. Check it out.