Running too warm.

[Mogordo]

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Hi all,
I'm looking for thoughts on my '83 Sentra wagon running warm. It used to run with the temperature gauge at below halfway and now it frequently goes past. I am attaching an image. The green line is where it used to run and the yellow line is where it started to get to now. I haven't wanted to risk it overheating so I turn the heat on before it reaches that point most times and it will come back down then. It's not from the fan not coming on, the fan will be running as it gets that hot. Does the yellow line seem too high to anyone else? The radiator is old but the fins don't look very damaged or dirty. I am wondering if it is that the water pump isn't working. For a while I was hearing a little kind of squealing noise that didn't sound like a belt and I don't notice it anymore. Would a bearing in the water pump squeal a while and then not seize up but fail otherwise? Anyone have reliable ways to check if the water pump is working?
Does anyone have ideas what is more likely the issue?
-Cari

[dlb]

I agree with you, the green line seems good and the yellow line seems a bit too hot. My first suspects with running hot are radiators and head gaskets. First thing I would do is a compression test to rule out the head gasket -- that's free and easy and gives you more information about what's going on. I would also take the belt off the water pump pulley and turn it by hand, it should spin easily. I have rarely found water pumps to fail, and when they do they usually start leaking from the weep hole as an indicator that they're failing (that's on Tercels anyway, not sure about your Sentra).

If both of those athings re fine, I would use a water hammer-style coolant flush tool on the radiator and engine block to clean out any deposits. I have one that I have used on multiple rads, blocks, and heater cores with great results. I think a lot of radiators get thrown out when they could be revived with a flush tool. If you go that route, make sure you get one that runs with an air compressor to create the water hammer effect. Otherwise it's just like running a normal hose through the rad which seems pretty useless to me.

[Ace]

Other possibilities:
Malfunctioning thermostat not opening fully. That would fit with your observation that running the heater helps lower the temp.
Inaccurate temp gauge reading, maybe due to failing temp sender unit (presumably electric?). Check coolant temp with a separate thermometer.

[dlb]

Other possibilities:
Malfunctioning thermostat not opening fully.

I could be wrong but I've always had the understanding that thermostats are designed to fail in the open position so that they when they fail, they only cause the engine to run cool and won't overheat it. That might be a broad generalization though.

[Mogordo]

Thank-you. I don't think it has any other common symptoms of a head gasket issue. How do you check compression for free? The one auto parts store around here that loans tools I asked about a compression tester for something on my Tercel and was told they don't have one in their loaner set. I think most water pumps do leak when failing, I had taken a quick look but the hole is in place that I'd have to wiggle around with a light a little to see and then I thought maybe some components could fail without a leak happening. But you are probably right about taking the belt off and checking the pulley. I keep thinking there would be a way to just determine if water is being pumped when it should be. I read of things like squeezing upper hose and feeling for a surge but wasn't sure how easy that actually is to feel and if I don't feel anything I won't know if I just didn't feel it or it actually wasn't there. My one sister said when the water pump on an '85 Golf failed years ago turning the heat on helped it cool down. I can look more into what would happen if the thermostat was stuck shut, I think it can get stuck open or shut, but the car isn't rapidly overheating so that doesn't seem as likely to me. I think the gauge is fine because it is pretty consistent and the reading lowers whenever I turn the heat on and lowers faster if I turn the heat on higher. I had a Corolla that had a guage that would read for a normal operating temperature then just suddenly jump to a high reading, then would sudddenly drop back to normal. That car didn't have any actual temperature issues.

[Mogordo]

But the radiatior seems more likely to be an issue to me.

[dlb]

How do you check compression for free?

Sorry, I assumed you had a compression tester. They're cheap though, and are an important diagnostic tool to have if you own old cars, so I encourage you to grab one.

[Mogordo]

When I was looking to borrow one I think the price was more than I wanted to pay but maybe if I looked around I could find one cheaper.

[Mark]

To do a basic diagnosis for a clogged radiator, run the engine until it shows the high temperature that the gauge has been showing you lately. Then feel the radiator with your hand. It should feel hot or at least very warm evenly all along the middle of the flow path of the radiator. On my '85 van, the radiator was cool around the middle section and hot only at the top and bottom. I took apart the radiator by unsoldering one of the end caps with a torch (I don't recommend doing this as there's a very good chance of destroying something beyond repair. I did it anyway since I figured it wasn't working anyway). Almost all the tubes except 2 at the top and 2 at the bottom were completely clogged with rust. It took me awhile to unclog them by pushing a thin strip of metal through them. I soldered the radiator back together and so far it's been working fine after a few days.
The other thing I'd do if I was you is to verify what the temperature actually is using a laser thermometer pointed at the hot side radiator hose or somewhere on the hot side of the radiator. It should be around 190-210 F or so. On my van, the temp gauge in the dash started showing too cool (about 1/4 on the gauge). I verified with a thermometer and an aftermarket temp gauge that I installed that the temperature was actually reaching 250 F or more, which is way too hot. After unclogging the radiator, the temperature is now normal although the factory temp gauge in the dash is still showing low.
I guess my whole point is:
-Verify what the temperature actually is since the factory gauge can malfunction over time.
-If the temperature actually is too high, check the radiator by feeling it with your hand to see if it is very clogged.

[Paul]

Something else to try when the engine is cool: remove the radiator cap and watch it warm up. First move a little coolant from the radiator to the overflow tank to allow for expansion. Start the engine. The coolant should be still until the thermostat begins to open. If the thermostat and water pump are working, the turbulant flow in the radiator should be noticeable as it approaches operating temperature. Eventually you'll have to put the cap back on to avoid boilover.
If its been more than a decade since the water pump was replaced, that plus a thermostat might be a good investment. They look cheap at Rockauto.

[Mogordo]

Thanks, feeling the radiator with my hand is a test I can do with what I have. I don't have a laser thermometer and don't know if someone I know has one but now I think I do see some of your and Ace's point about knowing what the actual temperature is.
I had this idea that I recently changed the water pump but couldn't remember actually doing it (sometimes I don't remember things it would seem like I maybe ought too...) and when I went to look at the weep hole more closely and then looked at the pump from under the car it looked very clean and new so I checked my records and I changed it last fall, about 20,000 miles ago, and the weep hole was leaking on the old one but is not on this one. I did loosen the drivebelts and found there is a little play at the pulley. Any thoughts on how much play there would be to indicate a problem? The belts didn't feel too tight to me, but I'm rarely sure, and I don't know what else would cause bearings to get worn that fast but with new parts these days I don't even quite count on them working correctly out of the box. If a little play is normal then it's more likely something else though.
Paul that looks like a breakdown of things I was reading on the internet but was unsure of. The way you wrote it out it looks simple enough. I guess if I put the cap back on the radiator as soon as I see movement it won't spill over but if I don't see movement will it be able to spill over or not? Will I then just have to make sure I don't let it overheat?

[Paul]

If you have a 180F/80C thermostat in your Sentra, you should have some time before reaching the boiling point. When you asked about checking for water pump flow, I thought this might be the easiest test. The more I think about your situation, I would try replacing the thermostat first.

[Mogordo]

I had asked my dad through e-mail what he thought but he is in a camping and not always checking communication devices way right now and it took him a few days to reply, I didn't know if it would be a week or more, but he too suggested replacing the thermostat first since it's pretty cheap and easy to do and not much loss if that's not it. I think I'll start with that, at least I'll know more one way or another then. I really want it to be something kind of easy to fix...Hehe
Thanks

[Petros]

coming late to your thread: you should replace the thermostat if it is over 2 years old, they wear out (and yes, they can fail by not opening all the way). it is a simple maintenance item, and likely the cause of the issues you are having. Buy a quality one, not one made in a communist factory (dealer parts is best, but any USA or Japanese made thermostat is usually good quality).

Water pumps rarely fail by not pumping coolant, usually they blow a seal and you are losing coolant. one time someone on this forum had the water pump impeller fall off inside the housing, but I have worked on cars of all types and ages since 1973 and never have seen that occur.

If replacing the thermostat does not correct it, replace the radiator cap (it regulates the system pressure, and they too wear out), and check the lower hose. it should be firm, if it is soft and squishy (or swelled up) replace it. the suction from the coolant pump can suck it closed, or near closed, at hwy speeds causing it to run hot.

the other common cause is a scaled and plugged up radiator, those can usually be cleared out by doing a white vinegar soak (fill it up with vinegar, allow to soak for 20 min, than flush it out, it should bring a lot of white/yellowish flaky material with it). if it leaks after that, you needed a new radiator because it was corroded too thin.

The cooling system in most cars is not that complicated, sort out all the components to verify they are working, and it should run cool. Regular maintenance should be to replace the coolant, radiator cap, and thermostat every 3 years, and the hoses every 7 to 10 years, or as necessary. If you have the type of radiator with plastic head tanks, those can decompose and blow out anytime after 10 years or 100k miles, and it is safest to replace them at about ten years old. Even so, we have a civic with one of those plastic and aluminum radiators, the factory one lasted about 20 years, than without warning it just blew off the top (severely damaging the all aluminum engine). Rebuilt head and new head gasket with a new radiator came later, but the lifetime guaranteed replacement from Autozone has been replaced (under warranty) once a year because it develops leaks at the aluminum fin/plastic tank joints. We are on the third Autozone radiator in three years. if you plan on keeping the car I suggest spending the extra money for an all metal radiator, you can get all aluminum welded performance radiators for most cars at a resonable price.

If you are losing coolant you have a leak somewhere, or you are losing it though a leaking head gasket (so it goes out the exhaust as vapor), or a bad radiator cap can allow it to vent out at too low a pressure. Pin hole leaks can be difficult to find, they might only leak under heat and pressure, so only vapor is seeping out, and you never see any liquid coolant.

Remember to ALWAYS diagnose the problem BEFORE you try to fix it! do not just randomly replace parts, it will only frustrate you and likely not fix it.

Good luck.

[Mogordo]

I sometimes do better to start replacing parts if they aren't hard or expensive to replace. If I think I have to diagnose a problem first sometimes I won't do a thing because I don't know how to diagnose the problem...
I replaced the thermostat, I don't know where it was made, it did not fix the issue but it may have changed it slightly in that the issue seems worse at highway speeds now. I am thinking the issue very well could be the radiator, it does look to have a lot of white build-up in it. I tried soaking it overnight in white vinegar but other than a very light milky color that was barely detectable being present in the vinegar nothing showed that the deposits were affected, no chunks, no looking grainy, no obvious discoloration. I didn't think to take a picture while I had it empty.
The lower hose could be slightly soft but I don't know what too soft is. But the issue now seeming worse at highway speeds does support that possibility. I replaced the radiator cap last year sometime.
Do you think the radiator being plugged is very likely the cause? It made sense to me but I found myself wanting to look inside a few other radiators for comparison in build-up..
The car has a manual transmission and I only saw one radiator available so far that I think is the right one just by looking at them. The ones listed for automatic do not look like what is in the car. Local stores rarely have access to a lot of the parts for this car.