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Subaru running a little hot

My 1998 Subaru Legacy L is running around 8-10º hotter than normal. I see this on my ODBC app on my iPhone. What is odd is that it is running hotter at higher speeds on the Interstate. The temperatures are well within what is acceptable for the Subaru, but run-on around 198-200º on the highway and tops at 205º.

An acquaintance who is a master mechanic didn’t want to alarm me but he thought I should check out head gasket leakage. I had already brought it into my mechanic this morning since I was having an unrelated problem (needed new battery) and he checked the coolant system. Didn’t find any problems but didn’t think of head gasket leakage.

My acquaintance recommended a cylinder compression test and to test the coolant for hydrocarbons. I had the head gasket replaced around 20,000 miles ago.

I noticed that my hood was not always properly down after a few drives. Could it being up a little affect aerodynamics and make the engine run harder? I didn’t mention the hood to my mechanic but he noticed and greased a cable that was making it harder to properly close the hood.

If I need a new gasket or take care of leakage I will probably buy a new car. Doesn’t make sense to sink another $1,500 to replace the gasket. I just put $700 into the car in the past month so it will pain me to do it.

One complication is that I need to drive around 12-13 hours at the end of next week to pick up my son from school. The drive is normally 4 hours each way but I was planning on visiting my father-in-law on the way back which adds 4 hours. I am wondering if it is not safe to drive this car for this long a journey. I don’t have any other car. I might be able to borrow a friend’s Toyota SUV for the trip.

Tomorrow I’ll look into testing for hydrocarbons and a compression test. Any idea how much that might cost?

Yes, also under inflated tires would make the engine work harder, and not knowing where you are, winter blend gasoline isn’t as efficient and engine works a little harder.

I don’t think you have anything to worry about.

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Thanks for the input. I checked the tires before I did any driving last weekend, they each needed a little air, so I can rule out tire inflation.

Interesting about winter blend. I’ve always felt that my car’s engine runs a little hotter in the winter but thought I was crazy. My mechanic mentioned that during the summer when I drive with AC on the cooling fans are on all of the time, without AC they only turn on when coolant temp reaches 192º.

My friend said the hood not being completely secure can be an issue. He also pointed me to testing kits and a page for diagnosing the problem (some issues beyond my means).

If you have the defroster on in winter, will the fans run all the time?

If you have the defroster on in winter, will the fans run all the time?

Way above my pay grade. The mechanic said that because the AC requires more work from the engine the fans need to run to try to cool the engine from the start and not wait for the temp to hit 192º. We were speaking of my car in particular, I can’t speak of any other.

I don’t see why the defroster would make the fans run since you are trying to keep the coolant hot so you can have hot air blowing on the windshield. I am referring to the fans that blow on the radiator.

Defrost mode usually engages the ac, and that turns the fans on at the radiator. This helps to dry out the air entering the cabin.

Ah, my car doesn’t do that. I need something newer perhaps.

It is an issue but should not have anything to do with the cooling system . Your friend is guessing . And if are concerned about using it on the trip just rent a vehicle.

On a 20 year old car it would be understandable to have some loss of cooling from the radiator. Internal corrosion leads to restriction in flow and externally, the fins connecting the tubes can separate, reducing cooling efficiency. The engine is working much harder at highway speeds. Although the amount of air is increased due to the speed of travel, it alone cannot compensate for the increased heat load from work being done. To me, this just looks like normal aging of a cooling system that is showing it’s age and will need attention in the near future. Keeping an eye on the temp will be important to avoid overheating as you know, these have some issues with headgasket sealing which you recently addressed.

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Thank you for your comments. I will try to stress less and keep my eye on the temps. If they stay where they are for the winter, great. If they increase, I’ll take action.

For reasons that have nothing to do with the condition of my car I need to buy a new one in the next 2-5 years. I was hoping to wait until my son finished school, lugging stuff from school to home, since I will move to a smaller car, but I am considering doing it this month. See if there are good end-of-year deals plus concern car prices might jump up soon. Looking at Subaru Impreza and Honda Civic.

Agreed. I replaced the radiator and the thermostat on my 1999 Civic in the last couple of years. There was a slight leak from the bottom of the radiator or its hose - I couldn’t figure out which and eventually replaced both. Less than $100 in parts. More recently replaced the stat with a genuine Honda after noting some temp fluctuations especially in extreme cold last winter.

Given how catastrophic a coolant leak can be, it’s almost preventative maintenance. Still, it’s important to keep an eye on the temp gauge. A warning light or buzzer could be an engine saver, especially for cars in their later years or drivers who don’t monitor gauges.

Slight overheating in Subarus is a tell-tell sign of the looming head-gasket issue, but it was addressed here, hopefully it is not that.
I had to replace radiator on 12-years old '96 Legacy since it was so much corroded and fins were so much damaged by the salt and sand, it was showing a temperature rise when driving in hot summer months. It was easy to do and very inexpensive to do in DIY modus operandi.

I replaced the radiator around 3 years ago. Total failure while driving. My mechanic tested the cooling system and didn’t see any problems. If the car isn’t moving, no problem.

This weekend I will test the hood being properly latched and test drive the Honda Civic and Subaru Impreza.

Growing up old school, it will stay the same, no problem or get worse, easier to find the problem. I would probably take the trip, knowing I have roadside assistance and can spare breakdown time if needed. Try a few practice road trips and see what happens, or rent a car. Our crystal ball cannot confirm one way or another.

It’s not doing any work then either so weaknesses in the cooling system are not necessarily exposed while idling.

So he did a flow test of the radiator? It’s not easy to test radiator flow. Radiator shops can do it. With the cost of labor today, most won’t even do a test because it’s often just cheaper to replace. Most mechanics will check the fluid level, the coolant ratio, the condition of the hoses etc but few will actually see if the radiator is flowing properly. Just offering up other potential causes so if you’re confident the rad has been ruled out, that one less thing to worry about…

Thanks for the ideas. I don’t know about testing the radiator flow but the shop is very good. Keep in mind that there are no warning lights going on and the dashboard gauge shows that heat is under control. I’ve just become so OCD on the subject that I monitor with OBD Fusion. I’ve discussed engine temps here I think 2 years ago and I know the car is within safe limits. But if the normal temp goes from 200º to 205º I will worry.

Yeah, you’re absolutely right to be keeping an eagle eye on it. These are the first signs of an issue developing…

Great, one less thing to worry about.
What about thermostat?

It’s OK. Was replaced with the water pump early this year. They checked it out this week.

All good ideas. I am much calmer about the car. Still need to test it out. I rarely drive during the week (mass transit for commuting) so I have to wait a few days.