Bad water pump...? Nope

3.4L, Toyota coolant mixed 60/40, Toyota Thermostat (180F), Water pump/timing belt kit replaced 4 yrs/15,000 miles ago.

I had a small coolant leak under the upper radiator hose where it attaches to the pump inlet. No leaks elsewhere. Upper hose is hot, lower hose is not. I suspected a bad thermostat and replaced it and the hoses after testing the new one. Tested the old one after replacement and it worked fine. Now there are no leaks but the difference in temperature is the same. I suspected an air lock in the block because I wasn't able to put back about a 1/4 of a gallon fluid from what I took out. Ran the truck with the front end parked on a snow bank for 10 min with the radiator cap off and I'm still unable to add more fluid. I do not see the fluid moving in the radiator to indicate that the pump is working. I drove it for about 15 min and the ECT registered 194F, it was -19F outside though. The fluid looked brand new with a minimum amount of debris, the heater works great, I don't hear a bad bearing... I'm out of ideas at this point. I've searched around in the forums but haven't run across a problem like this. Any help would be appreciated. Thanks in advance.

 

Congratulations, your engine is working perfectly! Hot coolant goes into the top of the radiator. Cold coolant comes out the bottom. The thermostat meters in just enough cold coolant to keep the engine at the correct temperature. So what's the problem??? Is it overheating?

 

>>I had a small coolant leak under the upper radiator hose where it attaches to the pump inlet. No leaks elsewhere. Upper hose is hot, lower hose is not.<<

Short tutorial:

The water entering the radiator should be hotter than the water leaving the radiator.

Hot water from the engine is pushed out the top, thru the upper radiator hose, and into the radiator top tank. Air drawn across the fins cools the water as it falls thru the radiator. It collects in the bottom tank and is pumped out thru the bottom hose, past the thermostat, into the water pump, and thru the engine where it is again heated.

During warm-up, the thermostat is closed and does not allow water to circulate thru the radiator. Instead, the water is simply returned to the block. As the engine heats the water the temperature rises. When the thermostat senses that the water temperature in the block is hot (~185-195 F), it opens to allow the water to circulate thru the radiator.

When you fill your radiator, fill it to where it begins to flow into the overflow container. Also fill the overflow container to about halfway between the upper and lower marks on that container. Put the radiator cap all the way on and start the engine. After running the engine at its operating temperature for a few minutes, turn it off and let the water cool a few hours until it reaches the ambient air temperature. Then you can check your levels. You will probably need to add more coolant, so do it through the overflow container.

Hope this helps you out.

 

It is not overheating, it’s running about 194F. I’m running it in the garage with a temp of 60F. I believe that there is no circulation of the coolant. When I say that the bottom hose is not hot, I mean it’s cold. While squeezing the hoses with the engine running no flow can be felt. I should also see fluid movement in the radiator with the cap removed, I do not. I’m thinking it’s a bad pump or radiator blockage at this point. Just looking to pinpoint it before ordering parts I don’t need. This is where the leak occurred, you can see the residual from the coolant as it sprayed out.Thanks

 

How long do you have to run it until it overheats, like 205F+?

That coolant may be flowing, just so slow that you can't notice it. The heater core takes heat out also, so turn the lever to cold to stop circulation through it.

 

sounds like the thermostat isnt opening or its opening but not very much...unless you have a higher temp thermostat. is it overheating or just getting to the 194?

 

Thanks for the replies gentlemen. I guess I’m underestimating how warm that lower hose will/won’t get even sitting inside for a few hours. I guess the truck sitting outside overnight with temps close to -30F will take longer to warm up than I’m giving it. I ran the truck for 45 min with heater off and on and I couldn’t get it any hotter than 194F. Hopefully the fluid pushing past the hose was an isolated incident. Thanks again

 

-30F is awfully cold!! When I was in Fairbanks a few years ago in late December, the temperature was -30F with no wind, and I almost froze to death while in a phone booth calling for a cab.

If your operating temperature is 194F then I wouldn't think you have a problem at all.

 

You can get yours to 194???? I live in Wyoming and it gets cold but not as cold as what you're talking about. Not for any length of time anyway. I've been thinking there is something wrong with my 2.7 because even in the summer it never gets hotter than about 184 degrees.In the winter it rarely even hits 180 degrees. I installed a grill cover and even with it completely closed it has to be well over 30 degrees just to hit 181 on the interstate or around 182-184 around town.

The only time I ever saw it hit 200 degrees was on a 100 degree day climbing a hill I shouldn't have been on and revving it over 4000 rpm trying to get up the hill. I guess 2.7's just run cool.

 

Do you know what temperature your thermostat is rated?

 

If it's leaking at the top goose neck/radiator hose and onto the timing belt cover, the spring clamp you have there is not providing enough pressure. Replace with a hose clamp.

 

Yeah I have that same problem, the hose clamps are worned.

 

Yea me too was leaking feom same spot . It was a loose clamp .

 

the purpose of the thermostat is to KEEP the coolant in the engine so that it can absorb heat. If the coolant flows too fast there is no heat transfer, same thing with the radiator.

 

I have no idea. It's the original thermostat. I'm guessing it's a 180.