91. 3.0 4runner just had top end done. Got it back and started to run hot again so I check thermostat and there wasn't one in it. Put one in and top hose gets supper hot and it starts to knock and I loose all power. Don't want to blow another head gasket. What to do

Have you checked the thermostat in the cooling system? When was the coolant last changed? Old coolant can collect dirt and clog up areas of the engine and radiator.
A thermostat is a simple valve the open when it gets hot and closes when it cools down. One that is old or sticking can cause overheating as it doesn't open and let the coolant flow through the radiator to cool it down. They are usually not very expensive and not a difficult job to replace.
A simple first check is to use the top and bottom radiator hoses. This check is easy, uses no tools and only costs the fuel you use to run the engine.
The Top Hose is the largest flexible rubber pipe that connects directly to the radiator, usually on one of the top corners. You will need to put your hand near the engine so BE CAREFUL!
With the engine cold, start the engine and gently hold the top pipe. It should be cold. Let the vehicle sit at idle and let it warm up to working temperature. Every 2 to 3 minutes check the top pipe again. If the thermostat is working after a few minutes the top pipe should start to warm up. it should get quite hot.
After about 15 minutes if the top pipe is still COLD *TURN THE ENGINE OFF!* You possibly have a faulty Thermostat.
If the top pipe heats up you can check the Bottom Pipe to see if it could be a Radiator issue. This is a pipe about the same size as the Top Pipe but it is on the lowest part of the radiator. This can be done with the engine OFF, once the vehicle is up to working temperature, (the Top Pipe is hot). Carefully reach down and grip it just like you did to the Top Pipe. This pipe should be warm but NOT hot. If this pipe is Cold you might need to get the radiator checked for damage or to see if it is clogged.

-Thermostat is not control the heater. It control only temperature in the engine.
-If you have no heater then check the following:
Make sure engine is cold before perform check.
-Check radiator is full of water or not. If not then fill it up
and try run like normal and turn on the heater.
-If now you have heat then you're done.
-But still no heat yet then cheek:
The heater valve. Is it open properly when you switch to hot or cold? If yes then NOT THE VALVE. Next lose both heater hoses from the engine and flush with garden water hose from one end and the other until you see water come out either end. Now connect back to the engine and top of the radiator more water.
You should be good to go now.

Good luck and stay warm

Mai

Is it possible you might have installed the thermostat upside down? How long was it hot? You might have burned your engine up. Check compression, each cylinder should be over 100 at least, and around 130 at best.

Sounds like you have an air lock in the heater, needs bleeding. From cold check and top up coolant, run engine without coolant cap put heater control to hot, watch the fluid level, will rise then fall suddenly when the thermostat opens, top up coolant and put the cap back on, later when the engine has cooled down again, check coolant level. Hope this helps.

Flushing a radiator at home is most often a waste of time. The chemicals used by a radiator shop are far stronger than anything you get at the parts supply house. What happens is that the flow you see is deceptive as the water tends to flow around a partial restriction and does nothing to remove it.
Though your garden hose has a lot of pressure it doesn't have the volume necessary. A garden hose will usually be sufficient to flush out a heater core though as it's smaller.
Have a radiator shop flush your radiator core and have a hydrocarbon test done on the cooling system to eliminate the possibility of head gasket problems. When re-filling the system, turn the engine off just before it reaches 210 degrees and let it sit for a few minutes so the thermostat can open, then continue filling. Always fill with the heat on high. Thermostat goes in with the spring end into the engine.Forget about the water pump...unless you got one made for a twin engine marine (CCW) application it has nothing to do with the problem though I've heard but never actually seen that the belt can be installed so it turns backwards.
When the engine is at operating temp cover the grille and force it to nearly go into overheat...the electric fan should come on and the mechanical fan should lock up to try to counteract that.
Don't open the system when it's hot (you found that out already). And, don't allow the engine to actually overheat.
My bet without seeing it? Likely a partially obstructed radiator. 4.0 engines make a lot of rust residue even when maintained. If that's what you have in there, or even the 4cyl. It is more than likely.

1. do it when cold(coolant)
2. if never done this before just follow thes step's
3. on radiator at bottom it's left side at bottom (face the car)is drain plug loosen to let some of coolant out dont have to drain all of it (gallon or so)
4. follow top hose to engine at end of hose will be thermosat housing it be 2 bolt's holding it on (1/2 inch socket )
5. before taking out bolt's take clamp off of hose & pull hose off.
6. now take bolt's out
7. lift housing off
8. look at how thermostat is in
9. take out thermostat dicard
10. clean gasket off of housing & engine block
11. put sealer on block & put thermostat in (same way came out)
12. put gasket on block & put thermostat housing on ,put bolt's in ,tigthen bolt's (20 flbs)
13. put hose on & tigthen clamp
14. close drain plug & titghen
15. top off radiator with coolant
16. crank engine , tpo off w/more coolant if need it ,let it run & come to temperture ,top off radiator again ,because when the thermostat open's coolant will begin to flow ,when full put cap on radiator ............DONE
17. JUST CHECK MAKE SURE NO LEAK'S

make sure you get ALL the air out run it without cap until you see water circulate turn heater to hot NO FAN ABOUT 5 MIN close cap ,see if that works

Please check that the electric cooling fan operates when the engine gets up to temperature. Quite a common fault.

When the engine is cool, open the plastic(black) drain at the bottom of the radiator. I should mention you'll need a drain pan, but, you knew that...lol. If you can jack the rear of the vehicle up a few inches this will help empty certain areas within the engine. Close the drain plug and fill with cool water, " DO NOT" put the radiator cap back on. Start the engine and turn the climate control inside to hot and "heat". Running the engine watch from out side the level will rise and drop when it drops keep adding water until the thermostat opens, you'll know by the temp of the top radiator hose. Let the ngine run for about 10 minutes, then turn off. Later, when cool again, drop the back end of the vehicle to the ground. Open and drain the radiator entirely. Fill with aproppriate amount of anti freeze, 4 cylinder 4 quarts, six cylinder 6 quarts etc. Run engine till warm again and themostat opens fill with remaining water. And top of the over flow tank. Cap off the radiator and you're done. Keep a close eye on the temp for a day just in case there was an air pocket in therre.

That's probably coming out of your coolant return bottle. With rad cap off & engine cool, look at your level in the rad, if necessary top it up to an inch or so from top. Start engine, turn heater(not defrost) on and let it run until up to normal operating temperature. Keep an eye on temperature gauge & rad level. When it's at normal, watch for good flow going through rad when thermostat opens. after flow slows down,(thermostat closes) top it up if needed. If you watch 2 or 3 times for flow, and gauge doesn't go over normal, then put cap back on, then fill bottle only to mark for warm or hot engine, with coolant. If gauge goes up over normal from there, replace thermostat, and I'd get a new rad cap too. If that has electric cooling fan, make sure it comes on shortly after you see thermostat open & coolant flowing through rad.