dfinn

1994 Pickup 3.0 v6
220k miles

Last week after about an hour of stop and go driving I parked my car. I walked away for just a minute and when I came back I could clearly hear the coolant rapidly boiling. The upper hose was so hot that I couldn't really touch it w/o feeling like I was burning my skin and the lower hose was hot but no where near as hot as the upper hose.

I dropped it off at the mechanic hoping it was something simple like the t-stat. He replaced that and flushed the coolant. He also pressurized the coolant system to check for leaks and didn't find any.

When I picked it up from him I took it for an hour drive on the highway. I parked it to check and the coolant was still bubbling. No where near as rapidly as the first time I noticed it but still enough to feel it if you had your hand on the upper hose and you could hear it if you really listened for it.

I took the truck back to the mech today. He used the sniffer to test for exhaust gas (CO2?) in the cooling system and did not find any. The truck runs fine, no hesitation or bucking and I'm getting normal gas mileage (22 - 24 MPG). The head gasket was replaced by Toyota around 140k. The mechanic says that he doesn't think it's the HG and that at this point the thinks it's OK to drive it.

I'm looking for a second opinion or possible suggestions for other things to look into. It seems to me like boiling coolant is not a normal thing and not a good thing.

Dan

Paul H.

I wonder if he used the right 50/50 mixture and the correct antifreeze. Also he may have put in a thermostat with the wrong temp setting in other words, its opening temp is too high for your coolent mixure.

dfinn

The boiling was happening before he changed the fluid and t-stat though. I don't know how old the previous coolant and t-stat were but I can say they were at least 1.5 years and 40k miles old.

mt_goat

Might try buying a new radiator cap, the rubber seal can get cracked and cause the cooling system to lose pressure. The coolant boils at a lower temp at lower pressure. I know you said he did a pressure test, but my guess is your old radiator cap was not included in the test. I'm not sure that's the problem but just one thing to check. Good luck.

chimmike

wouldn't be surprised if it was the radiator cap

86tuning

Yup. New cap = $15 from the dealership.

Could also be a failing fan clutch.

dfinn

Any auto parts store would carry that? Anything special I need to ask for?

dfinn

Mechanic did mention that the fan clutch was working but not quite as good as it should be. The fan clutch controls how fast the fan is spinning and/or when to kick in?

KevinInSac

It cold also be your driving habits. If you go from driving at really high temps, and running RPMs to just shutting her down, it can cause a boil over.

MudHippy

NAPA $6, IIRC.

MudHippy

Remove the ?, and there's your answer.

It'll still spin a little when it hasn't "kicked in", but when it's engaged it spins the fan faster.

ZUK

iTrader: (1)

Dan----That could be a clogged radiator. The 220K is the magic number that sees radiator problems. Upper and lower hoses should be equal in temp.
Do you notice that the temp creeps up some when on the highway?

ozziesironmanoffroad

sounds like the radiator cap all right. i had the same problem, i went to kragen/checker and bought an aftermarket cap for 8 bucks that locked and had a vent. works so much better with it. also replace all your coolant hoses and all that good stuff.

dfinn

Temp gauge seems to read right in the middle, not much variation on that. While talking to my mechanic he said that the next step would be pressure washing the radiator or sending it to a local radiator specialty place to have them check for issues. I'm hoping it's just the radiator cap, I'll pick one up tomorrow. If that doesn't work then I guess my next step is having the radiator itself checked out.

It was explained to me that the lower hose should be cooler than the upper hose. Hot coolant flows into the radiator through the upper hose, is cooled in the radiator and then flows out the lower hose. Is that not the case?

Thanks for all the tips everyone. Lots of good info on here.

mt_goat

Yeah...but Zuk may be right, the temp change of the coolant going through the radiator may not be big enough to notice just by touch with a free flowing system (t-stat wide open, water pump pumping, and unclogged radiator). Plus I'm guessing that when you were feeling the hoses the engine was off (mechanical fan stopped) or maybe just idling (mechanical fan spinning slow). In both cases there won't be a lot of cooling going on in the radiator without airflow.

What are the outside temps in your part of the world? How old is the radiator? If its the original rad I'd probably skip trying to clean it out. These Toyota radiators tend to get thin at the top and start developing pin holes and you can get a new aftermarket rad for $120 through places like radiator.com or the radiatorbarn.com

dfinn

Right now we are seeing around 80F during the day and 50F at night. Yesterday there was no boiling when I got to work or when I got home. Maybe this fixed itself. I'm still going to pick up a rad cap today on my way into work.

edit: as far as I know this is probably the original radiator. How hard is it to change the radiator on these? I've done it before on a few other vehicles so I'm not totally incompetent but I also only have basic tools.

ozziesironmanoffroad

not hard at all. if i remember correctly its 2 screws on each side of the radiator, then boom, down comes the radiator

dfinn

It seems like the new radiator cap has fixed the problem. Thanks to everyone for your help and suggestions.

thook

Sweet....

JoKEpLaYeR

260k was the magic number for me. Clogged radiator was my problem. Was boiling over and running warmer on the highway, it would cool back off around town.