Overheating/loss of coolant

Hello all, I have a 06 Tacoma 2.7L with 250,000+. It hasbeen a great little truck with no problems until now. Recentlyit has been over heating & loosing coolant and cannot find the reason why. Thereseems to be some backpressure pushing coolant into the overflow tank. The thermostat,hoses, belt, radiator cap & fan clutch have all been replace trying totrack down the cause.

I took it to a very reputable shop here in town thatspecializes in radiators and cooling systems. He did a pressure test 3different times and found no leaks (leaving the system pumped up for over anhour). Ran the truck and preformed a block test, no sign of combustion gases inthe system from a blown or leaking head gasket. No white smoke or coolantshooting out the tailpipe. The owner of the shop has been doing this for over30 years and he cannot figure out what is wrong. Yet every day the truckoverheats and I have to pull over and had 1/3 to a 1/2 gallon of coolant to getit back down to temp.

I really need the truck to last me a few more years and needsome help!!!!!!

 

So, it is probly overheating due to lack of airflow or lack of fluid flow....you have replaced or checked everything per your post except for those things. If it has a fan clutch check it, if the fan has been removed be sure it was put on the right direction. Make sure nothing is in front of the rad blocking air flow. Then if that is good it may be down to a plugged up radiator, given it has so many miles it may be time a rod out or new rad.

 

Sorry if this is a dumb suggestion, but the one thing I see missing from your list is the water pump. No leaks, holds pressure, but it is overheating. Possibly the coolant just isn't moving through the system at all? Bad water pump (yeah they usually leak when bad, but who knows)? Some other obstruction in the system?

Perhaps you've already checked - but make sure coolant is actually flowing.

Another interesting possibility is would running the heater reduce overheating - it is an alternate heat exchanger pathway. Might help find the problem.

 

Check the cap where he put the pressure tester. It may have a bad seal on it and it wasn't tested if the tester was in its place

 

My thought was to check out the water pump next. The thing that's got me is that I seem to overheat about 30 miles down the road pull over and have to add 1/2 gallon of coolant. If I've had a block test and passed that what could cause the back pressure issue? Not really sure what to do next. I plan on taking it to another shop to see on the off chance they may have seen something like this before.

Tried running the heater on high to help out, when the temp gauge goes up is seems to be due to only a lack of coolant in the system.

 

pressure is typically caused by the expanding heated water, it can be caused by the heat not being dissipated from the rad, the thermostat is stuck and not working causing a lack of flow thru the system or the head gasket is bad or a cracked block/head. A bad cap or sealing surface of the cap can cause the overflow too even tho the system is not over heated.
Heat not being dissipated is air flow thru the rad, either by something blocking the exterior or the fan/fan clutch not right. Did you check to see if fan is on right to pull air thru instead of reversed to push it out the front?
Or, lack of circulation. If the thermo is bad it wont circulate, if the rad is plugged up from being so old it wont circulate fast enuf to dissipate the heat.
The water pump is part of this sytem and could cause the lack of flow if it had its interior impeller rusted away to nothing I suppose, but in my several years of running a radiator shop I never saw that.

My gut feeling is plugged up rad or a head gasket issue. You could also remove the thermo to eliminate it from the equation.

 

Bleed the cooling system

 

Thanks for the help, brand new cap on the rad, brand new thermo & brand new fan clutch. No change. Pulling the rad and having it checked to see if it is blocked in any way. I hope that a new rad will take care of it (plastic tanks, can't really rod the old one). But if it isn't the rad, worried about a head gasket (don't really have the cash for that right now. First kid due in a week!).
Did another block test today and still all blue. Very weird. One quick note, when it does get hot and i pull the cap a bunch of steam comes out and the temp goes immediately back down to normal without me adding a drop of coolant (even though it's a 1/2+ gallon low.)

 

If you are adding a third to a half gallon every time it isn't a simpla e matter of the pump, the system doesn't need bleeding etc...

You are loosing coolant somewhere... If there is no visible evidence I would say the engine is sucking it up. Did he do the pressure test cold or hot engine. The head gasket may only leak when heated. It happens.

 

I agree, pressure test both hot & cold. It appears that the coolant loss is due to the backpressure out the expansion tank. I rigged up a little set up to capture what is going out the overflow port on the expansion tank and it overflowed that as well. That seems to be the main point of coolant loss. Now working on the why.

 

I'm going with the water pump being the issue.

 

What does your motor oil look like? You say you are losing 1/3 to 1/2 gallon. That's 42 - 64 oz. Are you having to add this daily?

Be it daily or every other day - whatever - that's a bunch of coolant and a visual of the externals should show something. If you are losing that much and can't see anything externally, you are losing it internally.

 

pull your spark plugs and check to see if one or more are really cleaner than the rest. if you find one theres your leaky cylinder. plugs get steam cleaned when this happens

 

No coolant in the oil, just changed it and looks all good.
Pulled plugs already, no coolant, not steam cleaned.
Coolant loss appears to be due to backpressure. Can hear it bubbling at the expansion tank even if the temp gauge reads normal.
Having rad flow checked today and inspection of water pump. Trying to rule out all possible cooling system items.

 

Sounds like you are getting close to finding the problem. Temp gauge normal and backpressure overflowing the expansion tank sure sounds like inadequate flow through the system. Bad water pump or other obstruction somewhere. Hope you've got it figured out soon!

 

Just got a call from the shop, rad seems to be "about 80% plugged up". Water pump seems to be okay. I sure hope this takes care of it!!

 

That's probably the best, lowest cost news you could get! Congratulations!

 

80% plugged rad? you found the issue for sure. Water can't circulate with the rad plugged up.