Heater / radiator issue - please help diagnose

My truck is losing heat when at idle. It will warm up, blow warm air, and then as soon as I pull up to a stoplight start blowing cold air.

It appears that the coolant level is also falling - going from the full mark to empty mark in under a hundred miles of driving. I cannot find any signs of leakage. Just did an oil change and I did not see any milky signs to indicate a leaking head gasket.

Running down city streets it is maintaining a coolant temperature around 186 degrees (ambient temps from 15-40) according to my scan gauge.

Anyone have a clue as to what the issue could be before I start replacing parts?

 

Once you fill the coolant bottle to proper level do you get heat? Can you get your hands on a pressure tester to pressure the sytem to check for leaks

 

If your losing coolant and no sign of leakage. It sure sounds like you have a blow head gasket, or worse. Could be block. I would check oil, for anti-freeze. Do a coolant system pressure test. Smell exhaust for sweet smell of anti-freeze.

 

I just borrowed a nice coolant system leak down test kit from Advance auto for a problem I'm having with my civic. I would try to do a pressure leak down check to see if you have a leak and go from there. Advance wanted a $200 deposit for the kit so take some cash if you want to try this

 

This happened to me, but not to your severity. I still had heat all the time, I just heard a gurgling from behind the dash when I got on the accerator. Turns out there was air entrained in my coolant, checked the overflow and it was dry.

I had no leaks into my oil, and as far as I know none into my trans. After 8 years but less that 30k miles, it just ended up this way. Same thing happened to wife's Odyssey. I was always under the opinion that the coolant never needed to be checked since it is a closed system.

I just topped off the overflow and now I keep my eye on it. Hasn't moved since last March.

 

I've been topping off the overflow. The coolant is definitely going somewhere.

Could it be a bad cap?

Doesn't help that it's below freezing most of the time, makes it hard to diagnose things.

 

No coolant in oil either. Just changed that.

 

Yes it could be a bad cap but you can test that with the coolant press tool

 

Somebody already asked if you smell the antifreeze; it would be a sweet smell. You haven't responded on that.

The smell would be richer with the heater on; and also does the windshield, seem to fog with the defroster on.

Both of the above, conditions, would indicate a problem with the heater core. Actually leak, in the core.

One more thing to confirm this, is to look at the heater outlet and the lowest point, at the floor. Do you see any signs of moisture?

You can't actually see the core; but these checks can usually point out a problem there.

If these things check out, go back to the engine and find the leak.

oldracer

 

This.

Note that coolant can leak onto the outside of an engine when warming up, then boil off. If that happens, you will not find it if you only look after it's warmed up. Took me a long time to find a leak that way. Different truck, but it was a loose hose clamp.

Not to be pessimistic, but there is an emerging trend of head gaskets going on the 4.0s from 03-06 on the Tacomas and 4runners. The gaskets were updated sometime during 2006. Most failures seem to be between 100K and 175K. Most people report the first sign being a miss during warmup and a check engine light/code referring to cylinder six. I hope that's not what's up with yours, but gotta mention it.

 

No smell or moisture.

 

If you haven't dumped the oil yet, send a sample to Blackstone and they will tell you for sure. Worth the $25.

 

Thanks, I just ordered the free kit. Glad I didn't dump it yet.

 

What about exhaust? I know maybe hard with cold weather. But see if anti-freeze smell there.

 

Sounds like a plan. We're in for subzero temps and snow so unfortunately I won't be able to do it until next week.

 

Nothing unusual with exhaust.

 

Really sounds like a weak cap, or maybe some dirt or something on the gasket surface.

 

What kind of influence does the reservoir cap have versus the actual radiator cap?

 

The reservoir isn't under pressure, so that cap is just a regular plastic cap (like your w/w fluid reservoir cap.

The radiator cap is more complicated with a rubber seal and spring to hold pressure, like a shaken soda bottle. If you took your cap off when the radiator was hot, the coolant would shoot out like Old Faithful.