Coolant/Heater problems.

[chuck0]

This is a '95 3.1L engine.
There are (2) issues here:

(1) I'm losing coolant & the engine temp eventually spikes until the radiator fan kicks in & brings the temperature down close to normal.
(2) The heater will not blow out hot air even when the temperature spikes.
It will blow warm air if the engine revs are boosted but air will almost immediately cool off when engine revs drop to idle.

I find no external leaks, oil looks normal and engine is smooth running.
I do have to add coolant to the radiator daily.
When the engine is shutdown I notice air bubbles coming up in the overflow tank for about (1) minute then stops bubbling.

Also, relating to the heater I see that the hose from the heater to the top of the water pump is barely warm. The other hose to the heater from the back of the engine to the heater is very hot.

I hope I've given a complete enough description to solve these problems.
Thanks in advance for any input.

[gmtech1]

Sounds like the heater core is plugged, causing the no heat condition. You can try backflushing the heater core, but it'll probably need replaced.

Also sounds like a lower intake gasket may be leaking, possible head gasket leak.

[chuck0]

The backflush sounds like a good idea.
If the lower intake gasket &/or head gasket were leaking, would I not have other symptons such as a rough idle, etc.?
Do you think a stop leak additive to the coolant is a good idea and if so which one would you recommend?

[GTP Dad]

If the intake manifold gasket were leaking you should see water in the oil. The oil would look like chocolate milk. If you detect this you shouldn't drive the car until you have it fixed. I also do not recommend the stop leak because it will make the issue worse and if coolant is leaking into the oil it can do a lot of damage due to its composition.

[chuck0]

The oil on the dipstick appears normal Not like choc milk.
i'm hoping that back flushing the heater core will solve both my problems.

[Tech II]

Can have a lower intake leak, and not have a chocolate condition in the oil, if it leaks externally, usually at the end of the lower intake under the throttle body......it will "pool" there in in the top of the engine....

Right now, it sounds like you have an air pocket, which is preventing flow through the heater core and causing the engine to overheat.....

The air pocket could be caused by a leaking intake gasket or a head gasket....

Can easily check if the heater core is blocked, by blowing thought the inlet(be careful of the antifreeze), with the outlet disconnected(the hose that was hot is the inlet, the hose that was not is the outlet).....

Do not use something like stop leak.....

The engine will not run rough if the coolant is not getting into the cylinders....for example, you could have a head gasket leak, that is real small, but there none the less.....parking the vehicle overnite, pressure might force a little coolant into a cylinder....when you start the vehicle, you might have a slight misfire in that cylinder at first, and then it clears up.....if it is a real bad leak, then yes it would be constant....

[chuck0]

Will check under throttle body & gasket perimeter.

[richtazz]

My vote is the intake manifold gasket has failed. The most common place they fail is the seal around the coolant ports at the ends of the manifold which are right next to the intake ports. The coolant is sucked into the cylilnder and may not be to a degree that will cause a misfire, but enough that over time will cause significant loss of coolant. Also, I agree with Tech that the heater core hose temp issue is being caused either by an airpocket or low coolant system pressure caused by the leak.

[bozr]

Another vote for the lower intake gasket. They can suck coolant directly into the intake port and only drip a small amount into the crankcase. The oil will look perfect, until you take off a valve cover and see the coating of cream colored goo. Check the bottom of the oil filler cap for moisture or an oil/water mix.

Check the coolant level at the radiator cap (cold). If it's low, open the two bleeder screw and fill it. Close off the bleeders when coolant flows from them. Start it up check the coolant level again and put the cap back on. If you get heat the heater core is okay the lack of it was from low coolant.

Check the torque on the lower intake manifold bolts. you can get to 7 of the 8 bolts without removing anything. If they're loose tighten them up. As the gasket deteriorates it can lose bolt torque. Not a fix but you can confirm it's the LIM if the leak slows down. At a certain point the seal blows off the surface of the gasket from coolant system pressure.