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Subaru running hotter after new timing belt

1998 Subaru Legacy L.

I had my car’s timing belt and water pump changed at 107,500 miles (the timing belt was previously changed at 40,000 miles when the water pump had a leak).

On Saturday I noticed that the Subaru’s engine heat was 5-10 degrees warmer than normal. I use an Automatic plugged into he engine diagnostic port that reports to my iPhone. The dashboard temp gauge was fine. Previously the engine temp would be 178º or warmer, usually in the lower 180s on the highway and going up to the 190s in local driving or after going uphill on the highway. But always lowering to around 180 on level or downhill highway driving.

On Saturday, once the engine warmed up, it would not go below 189º and usually between 192-196º. At a red light it might go up to 199º (only went up to 201 or 202º once or twice). No huge jumps in engine temp (that happened last year).

Last year I had the head gaskets replaced and initially noticed higher engine temps but after a week the engine ran cooler. Saturday was a cool day and I notice that the engine has run hotter on cold days on occasion.

The engine temp is within normal operating tolerances. I realize that the coolant might be different than before and that the new water pump has a new temp gauge.

I am just wondering if I should be looking for anything, or if the higher temps continue should I bring it back to my garage (they are very good), or just not worry. The one thing I need to check is the coolant levels. Despite driving these years I am going to classify myself as a novice in diagnosing auto problems.

Check the coolant as there may have been an air bubble in the system. They usually work themselves out over a few days, and the coolant would go down in the overflow bottle. All normal. It sounds like you’re very careful watching the temperature, so you saw something most people never know about.

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Its possible your old thermostat was failing (they usually fail open) and was replaced with the timing belt. I believe this engine should normally run in the 199-202 degree range. 178 F is too cold and indicative of a failing thermostat.

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Thanks. Both of these replies make me feel better. The air bubble makes sense in that it would explain what happened last year.

The water pump thermostat was replaced (my mechanic said they always replace this with the water pump). But I don’t know if this is the thermostat used by the diagnostic port. But even if different a failing water pump thermostat could have made the engine run cooler.

For me, the main thing is knowing that what I am now seeing is normal. I am hypervigilent on this issue due to overheating issues a year ago (which was identified and fixed).

The thermostat controls the entire temperature in the engine no matter where the sensor that measures it is so your reading off the iPhone is as correct as you can get. Besides, this is the temperature the engine uses to determine how to make it run properly. To get the proper amount of fuel, the engine’s computer must know the water temperature and at is what your iPhone app is reading. As long as the temperature stays below about 245 F, you are fine.

Even if it gets close to that, you can turn on the heater at full heat, full fan and that will bring the temp down pretty quickly so you can safely pull over. That way you can catch any problems before the engine is damaged.

I used to do that with my 1973 Chevy Suburban. Of course all I hd was the dash temp gauge.

Thanks again.

The coolant level should be checked the day after a cooling system repair and if a problem is suspected the coolant level should be checked asap.

I do not have answer to your question but I am curious to know the kind of unit you have plugged into the OBD port. Will be great if you could share the link of the product. Thanks in advance.

I am not familiar with the on e the OP is using but Torque and Torque Pro (for Android) have this function. Full trip computer, 0-60 and 1/4 mile times, HP and torque peaks as well as display of anything they can grab off the OBD2 data stream.

Sorry, I should have been more clear. I am aware of the application. I would like to know the hardware. I have had serious bad luck with OBD readers I got so far, none of them worked.

ELM 327 compliant Bluetooth OBD2 reader. I have 2 and one will not work with my phone but it works great with my Android tablet the other works with my phone. At $5 - $10 each, they are a bit of a gamble. Get the app and see what brand IT says you should buy.

Exactly, I am looking for the brand only, as all I got were ELM327 compliant ranging from $5 to $20 and none could work with my phone, android, Samsung S4

I have a Samsung S4 mini… I bought THIS and it works great;

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I use Automatic hardware, 2nd generation. I use the Automatic app for general stuff and OBD Fusion for all engine info, MPG, etc. I have been very happy with it, occasionally I need to unplug the Automatic hardware and plug it back in, I try to do it weekly so I won’t have to do it when the engine is running. Problem here is that bluetooth is a technology that claims “see how great the next version will be.” The 1998 Subaru diagnostic port is a bit funky, I used to use another device that required special settings for my car and often gave me problems.

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I used to have 1996 Legacy L, which was quite cheap to buy as it had a number of issues of “not critical, but definitely a headache” type

one of them was slight overheating as you pointed, but also it was somewhat unstable idle, like if one side of opposite engine fires with more power than another. compression meter showed 10% lower compression on one side, wet test did not have any difference to dry test.

long story short: previous owner replaced timing belt (it was brand new) and they misaligned one tooth on one engine side. once I corrected, my compression got back to even in all 4 cylinders

check if whoever was putting that new belt on did not misalign it.
it might be not necessarily misaligned on camshaft side like I had, but on crankshaft sprocket: that would keep idle stable, but could explain slight overheating.
considering you have something like 50 or 60 teeth to count on each side, I can imagine it is possible to make a mistake

if it is 2.2L engine - it is non-interfering and overall very forgiving one.
easy to open plastic shield in front and check belt alignment marks

I recall using a simple adjustable wrench to get to alignment marks, then ballpen to mark and count teeth, making mark every 10th tooth. one side showed one tooth off for me, fix was blazing fast to get auto-tensioner compressed and anchored, then carefully getting one tooth moved, then releasing auto-tensioner

[addition] it is very tight in the front of the engine, so I had to remove electric fans and use a piece of plywood to protect radiator from kicking it with tools

Thanks for this suggestion. I have car knowledgeable friend who can help me check this out in exchange for beer (no drinking until after the check). This is the 2.2L engine.

I checked my gas mileage for my normal Sunday drive. 30-31MPG compared to 32-33MPG that I normally get. However, traffic was worse than normal and could account for poorer gas mileage.

I checked coolant level last night. The radiator was full and the overflow tank was at the proper level.

The car is running very smoothly. I suspect this new temp is simply the new normal or due to a bubble. My mechanic is very good but mistakes are always possible.

Is the compression difference possible to detect using ODB Fusion (the motor monitors this itself) or is this something that requires attaching a gauge to the motor?

compression is not something you diagnose over OBDII, you have to go with spark plugs removal and use proper tool to measure. since you car runs smoothly and you get the MPG you report, I would not assume it to be your issue.

I was finally able to find instruction for belt alignment:

this instruction is even better, as it tells actual teeth counts for 2.2 and 2.5 SOHC engines:

Z1: 44 tooth length on all 2.2L engines and 2000 2.5L engines and 46.8 tooth length on 2001-04 2.5L engines
Z2: 40.5 tooth length on all 2.2L engines and 2000 2.5L engines or 43.7 tooth length on 2001-04 2.5L engines

That “half-tooth” is what played a nasty trick to the car I used to own

Thanks again for your impression. I know my mechanic will drive a car after working on it (they’ve spotted problems that way). So I will put this in the hold bin for now and bring it up with my mechanic if I think there is a problem at my next oil change. Like I said, I am quite an amateur at this stuff (though I did rebuilt the carburetor of a 1973 Chevy Suburban back in 1984).

I concur w/ @Mustangman 's advice above, if the water pump and thermostat got replaced along w/the timing belt, that’s what is causing it to run a little warmer. And I’d guess it was running at too low of temperature before, and it is now running at the correct temperature. As long as it seems to be running well, dash temp gauge reads ok, not losing any fluids, you are good to go. And you’re probably getting better mpgs too.

Again, thank you to everyone for their comments.

To my surprise the Subaru was running a little cooling than yesterday. The minimum engine temp was 183º (though usually higher) instead of 189º, so I suspect that air in the coolant was/is a factor. Overall the engine is running warmer than before the timing belt/water pump replacement, frequently at 190º instead of 185º. I am now comfortable with that.

Yesterday’s drive was a more normal one with decent traffic in both directions (combination of I66, I495, I95 (Maryland), MD 29, and MD 32) and with an average of 33MPG. So similar MPG as a month ago (I was hoping that would improve). When the car stopped the engine temp rose slower than last week, and last week I thought it was acceptable. The car runs smoothly. The dashboard engine gauge has always been a little below 1/2.

So I am happy and will not pursue this anymore.