I have a 1993 toyota pick up, 22-RE, 5-speed. Lately its had an overheating issue. It seems like its building too much pressure and spitting coolant out of the radiator cap, or it'll build too much pressure and pop the cap on the plastic overflow tank and start spitting out coolant there. At that point the temp shoots through the roof. I'm trying to figure out if this is maybe a thermostat issue or possibly an issue with the water pump, or both. Any feedback would be appreciated! Trying to get the issue resolved asap. Thanks....

 

Might be the thermostat, much more unlikely to be the water pump.

Sadly, might also be a blown head gasket.

 

I replaced there thermostat yesterday and had the same problem this morning with the cap to the overflow tank popping off. If the water pump was going bad would it cause too much pressure in the cooling system to pop the cap off like that? Also, if it was the heat gasket what other symptoms would the truck have??? Thanks!

 

Make sure the vent to the overflow is clear, same size as the input hose so shouldn't be building any pressure.

Have your radiator cap tested.

Run the test on the radiator for combustion byproducts.

 

^^ Yes, do this!

Pressure is building in the system. Now you need to figure out if the pressure is naturally building in the cooling system but over pressurizing itself or if pressure is leaking its way in to the cooling system from the combustion chamber.

A water pump cannot cause over pressure problems if everything else is working properly.

 

 

It's not a Sprague clutch but hydrolic thermo coupled device it'll spin both ways..

If it's not getting tougher to spin when heated it's a sign it's time to replace it.

 

Does it start to get hot before or after the it boils over? If it gets hot after then that's usually a sign the radiator cap is bad. Check to make sure both seals are in good shape and the spring is fine. Also make sure the sealing surface on the radiator are clean and flat. It will leak if its not.

Start the engine cold and keep an eye on the coolant in the radiator as it warms up. You should see some obvious coolant flow when the thermostat opens. If not, either the stat is stuck closed or the pump isn't pumping. Usually when the pump goes, it will start to overheat withing a couple of minutes of starting cold due to hot spots in the engine. It needs to have constant coolant flow to keep the hot spots down.

Make sure the fan is hard to turn when its hot. If its not, replace the clutch. It can spin both ways. Do you have the fan shroud installed.

Make sure the radiator and condenser are clean. If they are packed full of dirt and bugs then they won't cool. Even a thin layer of dirt on the fins creates an insulating layer and reduces cooling.

How are the radiator hoses? Keep an eye on the lower. If there's restriction in the cooling system it can sometimes collapse and block all coolant flow.

As said before, it might be a good idea to get a block tester. Its a devices that sucks air from the radiator through some blue liquid. If it changes from blue to yellow you have more serious issues to deal with.

 

Head gasket would affect compression readings. If you check those, that be a way to know. Scary...air bubbles in the rad...thats a positive confirmation if you did a leak down test and got those results.

Hopefully just a failing rad cap. Go for that first. Maybe clamp on the overflow hose for more secure hold. Bubbling there too? HG...more likely. Other obvious sign is continuous white smoke out the exhaust.

Better carry some extra distilled h20 and some thick rags/towels. Avoid warping the block/head or being stranded!

 

Substitute "would" with "could" and its a true statement..

If you look at this post, you'll see I had coolant to combustion chamber leakage on number 2 and no notable effect on the compression test reading.

Bottom line is don't guess test!

In the above scenario of my breach it failed an audbile check...

 

Actually from reading that thread, you mentioned 120 is on the low end of the range for comp readings for your model, so I'm not convinced. I bet after you replaced the HG the readings were much higher then?

I would definitely suspect low range readings would be a tell tale sign the HG is about to go. And it looks like in that case, it ended up being.

But in the unpredictable world, of course I should go back and go with 'could' wording. Let the record show that what I meant to put instead of the previous is the word 'could'.

Lets just hope for the original issue here it is not.