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Engine overheating, fan's don't turn on unless AC is on, but still overheats even then?

I’m not an experienced mechanic but I’m trying to figure this out and have been doing hours and hours of research. The car is a 1995 Honda Accord Wagon

The main problem is the car is overheating when it runs for about 10 minutes or more. The heat also does not work and has not worked for some time.

This seems to be exacerbated by the fact that the fans are not turning on as it gets hot. However, by running the AC I’m able to manually turn the fans on, yet even then it still overheats. Maybe a little bit slower, but it gets up to the red still.

I have flushed the coolant to make sure there are no air bubbles and changed the thermostat. I switched the fan relay for the power window relay, which seemed to work, and there was no noticeable difference in the fan’s function. The fans seem to run every once in a while but it’s unpredictable and erratic.

Something to note is that I was testing things and got it to a high temperature and the fans didn’t come on until it was jostled by me closing the hood.

Also when I drained the coolant there was a lot of rust/grit/black stuff in it. I believe this has probably plugged the heater core and causing the heat not to work most of the time? Is the solution to simply replace that?

So my theories:

bad water pump?
radiator is too full of grit and not flowing fast enough? (radiator outlet hose doesn’t seem like it’s too hot, though)
fan switch could be bad?

Any other ideas? Very much appreciated!

It’s impossible to tell whether that is the solution. But I can tell you what to check to find out.

You need to check the radiator for flow and even and decent heat dissipation. In a car this old that may be one of your problems.

You need to check the water pump for flow.

You clearly need to check the cooling fan temp sensor and the fan relay. Clearly the fan should be coming on.

Under the circumstances, I’d also perform a cylinder leakdown test to see if I had a breeched headgasket. Or, at least, test the coolant with a lab strip to check for the presence of hydrocarbons.

The rust suggests that you routinely have air voids in the system. Improper purging & filling, allowing the coolant to run low from a leak, or even combustion gasses from a breeched headgasket could all share blame.

I’d go with the possibility of a leak. Perhaps from the water pump. The shaft seal can begin to leak when the pump gets old, and it often won’t leak unless the pump is turning. When the coolant contracts during cooling, it may be drawing air in through the leak, causing the voids that are causing the rust.

You need to change the T-stat and radiator pressure cap too, but because you have rust in the system I suspect your problems are serious enough to want to know before spending the cash. These are NOT causing your problems, although they may be contributors, or may even be the initial failure that caused the chain of failures. .

I’d start by checking for a headgasket leak. If you have one, you can them decide whether it’s worth it to you to repair it. That’ll be the most expensive item to fix, so start there.

Or simply drop it off at a mechanic or radiator shop and ask for a “diagnosis only”. A few hundred up front might save you thousands in the long run.

The coolant temp sensor is at the bottom of the radiator. If thst much crud came out, you may need to have the radiator removed and run through an ultrasonic bath to get all the crud out. It is probably insulating the sensor and blocking critcal flow.

Thank you, this is very helpful. I’ll try to report back about how this turns out.

If it has the original radiator, it might be time for a new one, especially it it was full of crud. It has lost its ability to transfer heat. They are only a little over $100. A good flushing of the heater core to see if that can be salvaged.

Just to clarify, I meant to call it the cooling fan temp sensor.

It might be possible to have the heater core reversed flushed and bring the heat back to the passenger compartment. If the heater core is plugged up, the radiator is probably too. Might be a good idea at this point to just purchase a replacement radiator. The radiator fan should probably be coming on after the car has idled 5-10 minutes. If it isn’t, it is probably the fan temp switch that is faulty. That is inexpensive to replace. Given all the cooling relating issues, consider taking the car to your local radiator shop and having it diagnosed and fixed there. They are the experts on all these kind of problems.

The water pump is driven by the timing belt and it should be changed when the timing belt is changed, every 7 years. If your due for a belt, you might just as well get this service done.

If the water pump is less than 7 years old, then it should be OK. You may not be actually overheating, maybe the ECTS is not working correctly, you may want to change it. If you know anyone with a non contact IR thermometer, you could read the temp of the block right next to the ECTS to get an idea if it is off.

There is a heater control valve located in the heater lines just in front of the firewall. On this model, the cable that is supposed to close this valve when you turn the heat all the way down for AC in the summer doesn’t work very well. It is possible that a previous owner disconnected the cable and closed the valve all the way to get better AC in the summer. The heater hose comes out of the engine just under the distributor so you can follow it to the valve to check. There is another place to disconnect the cable at the blend doors under the dash but that is more work in my opinion.

You say you flushed the system, did you bleed it afterwards? Are you using coolant, the engine will overheat with plane water. It has to have at least 25% antifreeze in it, 50% is better.

Excellent ideas @keith ! Good post.

I’m thinking that if it only takes 10 minutes for it to overheat, what we are really looking at is a head gasket, and not a cooling problem.

A car that is almost 20 years old is a prime candidate for a bad head gasket or other combustion leak. This is easily confirmed with a chemical block test which can be performed by your mechanic or you can purchase the kit at NAPA Auto Parts and do it yourself.

Yeah, thanks everyone for the input. Turns out it’s the head gasket. I took it to a mechanic to confirm and there is pressure building in the coolant system. :frowning:

Now to figure out if it’s worth it to me to fix it or sell it as is… I appreciate all the helpful comments!

This is a very easy engine to work on. My vote is to fix the car.

Make sure the head and deck aren’t warped, before throwing a new head gasket on it

Have the machine shop check it out, and “clean up” the head as needed

While you’re at it, here’s what else I would do

Timing belt
timing belt tensioner
timing belt idler
water pump
radiator cap
cam seals
crank seal
balance shaft seal . . . if your engine has one

Many of these things have to be removed anyways, if the head is coming off

I know this may be kind of extreme, but you may want to consider a valve job