Coolant mix is likely source of heater problem

Hey there, time traveller!
This article was published 17/12/2004 (7643 days ago), so information in it may no longer be current.

QUESTION — I am having some heater problems with my 1990 Dodge Caravan.

The temperature gauge wasn’t coming up as high as it used to and there was little heat inside the van. I was told I should install a new thermostat. I did that and the temperature gauge now comes up to the normal position but there is still poor heat inside the van. If I leave the van idling for a while, the temperature gauge actually climbs into the hot range.

I changed the antifreeze at the same time I put in the new thermostat. The owner’s manual says the cooling system holds 14 litres of coolant, and after draining the radiator I added seven litres of antifreeze and topped it up with water. Could it be that the antifreeze and water are not mixing inside the engine? Any help for a shivering driver would help.

ANSWER — I suspect the antifreeze and water mix is your main heating problem. The cooling system for your van holds 14 litres of coolant, but when you drain the radiator you will only remove about nine or 10 litres. The remainder of the coolant is trapped in the engine. When you refilled the system, seven litres of antifreeze were added but only about two or three litres of water were required to top up the system. The coolant contains too much antifreeze!

The antifreeze cannot transfer heat as well as water can. As it passes through the engine, it is slow to absorb heat. As it passes through the radiator and heater core, it is slow to release heat. Most antifreeze manufacturers recommend a 50/50 mix of antifreeze and water, but follow the instructions for mixing on the jug. A 50/50 mix should protect the engine down to below -40C. It also protects in the summertime because the mixture has a higher boiling point than just water.

Drain your cooling system again and measure the strength of the antifreeze solution. I am sure you will find it too strong. Add water to the drained coolant until it is close to the desired strength and then pour it back into the cooling system. After running the engine you may find it still measures too strong. Drain a little more and top it up with water. You can drain some more and try again, but I try to make an educated estimate and mix it a little on the weak side so it will be correct when reinstalled.

You may also have a restriction in the heater core or heater hoses on your van. Feel the hose temperature. The inlet hose should be hot and the outlet hose slightly cooler. If you find a big change in temperature anywhere in the system, it indicates a blockage. You may need to replace the hoses or heater core, but start with the cheapest repair — the correct coolant first.

QUESTION — I have a 1982 Pontiac Firebird with a three-speed automatic transmission and V8 engine. When I pass another car and hold the gas pedal down all the way, the transmission doesn’t shift from second to third gear no matter how fast the car goes. Recently it has also had trouble shifting down into lower gears as I slow down. I was told I needed a new transmission, but they couldn’t guarantee they would fix the problem. Will a new tranny fix it or should I consider selling the car?

ANSWER — The transmission throttle valve cable is the first place to begin when checking out your car problems. It sounds like the cable is binding inside its sheath and causing the transmission to shift erratically. The cable can be removed from the carburetor linkage and moved by hand. It should move smoothly with no binding. Replacing the cable can be done without opening up the transmission.

If the cable is fine, the throttle valve in the transmission valve body may be sticking. This requires removal of the pan and valve body only; not the whole transmission. This should be a fairly simple problem to correct. Keep the car.

Jim Kerr is an experienced mechanic, instructor of automotive technology and freelance journalist. You can e-mail questions to Jim at the address below.

kerr.jim@sk.sympatico.ca