Overheating Problems - Possible Causes?
#1
03-05-2012, 03:28 PM
Overheating Problems - Possible Causes?
My 1990 has been overheating some lately (Hawaii where it's still in the 60's and 70's)
It runs fine on the highway and roads during normal use, but during rush hour it will overheat, and once the temp gauge gets to about half way it will stall out, and refuse to start until it's cooled off some.
I'm a little stumped as to why it's happening. The coolant doesn't look overly low - it's about half way down the reservoir, but still above the low line. I'm going to try to top it off, but the guy at O'reilies didn't know what kind of coolant I needed, so I'm going to have to look it up in the manual when I get a chance.
Barring coolant - is there anything else I should check? I changed the oil relatively recently, and it doesn't look low, and the clutch seems to be properly adjusted.
Edit: I do hear the radiator fan come on from time to time, so that's probably not broken.
It runs fine on the highway and roads during normal use, but during rush hour it will overheat, and once the temp gauge gets to about half way it will stall out, and refuse to start until it's cooled off some.
I'm a little stumped as to why it's happening. The coolant doesn't look overly low - it's about half way down the reservoir, but still above the low line. I'm going to try to top it off, but the guy at O'reilies didn't know what kind of coolant I needed, so I'm going to have to look it up in the manual when I get a chance.
Barring coolant - is there anything else I should check? I changed the oil relatively recently, and it doesn't look low, and the clutch seems to be properly adjusted.
Edit: I do hear the radiator fan come on from time to time, so that's probably not broken.
#3
03-05-2012, 03:56 PM
February 2012 ROTM
#4
03-05-2012, 04:01 PM
#5
03-05-2012, 04:13 PM
February 2012 ROTM
Bad radiator cap
The radiator cap does several things. It
seals the system against the outside world (main seal function)
keeps the system pressurized when needed, so as to raise the boiling point of the coolant
allows excess pressure and coolant expansion to vent to the expansion reservoir (pressure seal function)
allows coolant to return to the radiator when the engine cools down (return seal function)
As you may have gathered from the above section, the radiator cap has three seals, any of which may fail independently of the others:
The main seal is the one that seals the cap against the top of the filler neck. Just a rubber gasket that operates just like one on the lid of a pickle jar. Simple and reliable.
A failed pressure seal will allow the coolant to boil at a lower temperature, and coolant will be able to travel freely and foamily to the expansion reservoir. This will cause localized hot-spots inside the engine, which can lead to premature head warpage, and may hasten head gasket failure. It will also cause the rad coolant level to be low, just like a failed head gasket.
A failed return seal will prevent the coolant from returning to the radiator as the rad cools off, causing a vacuum that can collapse the radiator's hoses. This will prevent the coolant from circulating if the hoses don't re-expand as the engine warms up.
A bad rad cap can cause similar symptoms to a failed head gasket, so it's a cheap first step to try before bringing it in. If you replace the rad cap and you still have bubbles in the coolant (or foam in the reservoir), then suspect the head gasket.
If the engine starts to overheat at idle, or in heavy traffic, and the gauge goes down when you rev it, the coolant is probably low.
Moreover, a neglected cooling system can load up the cap with crud and corrosion, preventing proper coolant flow in and out through it. Peel the seals back with your fingernail to check for goop. If you find any, a blast with a garden hose and probing with a toothpick should clear most of it out.
But anyway, a new rad cap is less than $20. Make a habit to change it every 5 years, just in case. It's pretty important.
--------------------------------------------------------------------------------
Bad thermostat
This part is the traffic cop that controls when the coolant is allowed to circulate and when it isn't. It's the device that's meant to quickly allow the engine to warm up to its design temperature, but no hotter than that.
Thermostats can stick shut or open, get lazy, or fail to open at the correct temperature. Depending on how and when they fail, they will cause either overheating or underheating. Overheating usually happens when the thermostat fails to open, or fails to open enough. If it fails to close, the engine will run too cool, causing all sorts of other problems.
A cooling system full of rust, scale, silt, or gel will interfere with the thermostat's operation, causing even more cooling problems. Gunk can plug up the thermostat, causing overheating, or make it stick open, causing underheating. Incorrect installation of the thermostat (can be done, even by professionals!) will also interfere with thermostat operation.
Normally mounted in the top of the lower rad hose in modern Hondas, the thermostat senses engine heat in the coolant. It is supposed to open up when the coolant in the block has warmed up enough, allow the cooled coolant in the rad to flow into the block, pushing the hot coolant from the block into the rad.
When the thermostat is closed, a small bypass hose allows coolant to circulate through the engine block, around the business end of the thermostat, through the water pump, and back around again. This keeps block temperature even, and helps the thermostat warm up as well. Once the thermostat opens, the bypass is closed off by means of a special extension on the bottom of the thermostat.
Aftermarket thermostats are highly associated with overheating and underheating. Most Hondas require 78C (172F) thermostats (that's the opening temperature). Too many aftermarket thermostats are wrongly rated for your car and are poorly made. Your emissions system may not work correctly with a different rating installed. In addition, some aftermarket units lack a bleed hole, the absence of which can trap air and lead to overheating.
A new genuine Honda thermostat is about $30 and is guaranteed to work properly in your Honda. In my mind, it's foolish to trust such an important job to an aftermarket part. Changing it every 5 years is excellent preventative maintenance.
The radiator cap does several things. It
seals the system against the outside world (main seal function)
keeps the system pressurized when needed, so as to raise the boiling point of the coolant
allows excess pressure and coolant expansion to vent to the expansion reservoir (pressure seal function)
allows coolant to return to the radiator when the engine cools down (return seal function)
As you may have gathered from the above section, the radiator cap has three seals, any of which may fail independently of the others:
The main seal is the one that seals the cap against the top of the filler neck. Just a rubber gasket that operates just like one on the lid of a pickle jar. Simple and reliable.
A failed pressure seal will allow the coolant to boil at a lower temperature, and coolant will be able to travel freely and foamily to the expansion reservoir. This will cause localized hot-spots inside the engine, which can lead to premature head warpage, and may hasten head gasket failure. It will also cause the rad coolant level to be low, just like a failed head gasket.
A failed return seal will prevent the coolant from returning to the radiator as the rad cools off, causing a vacuum that can collapse the radiator's hoses. This will prevent the coolant from circulating if the hoses don't re-expand as the engine warms up.
A bad rad cap can cause similar symptoms to a failed head gasket, so it's a cheap first step to try before bringing it in. If you replace the rad cap and you still have bubbles in the coolant (or foam in the reservoir), then suspect the head gasket.
If the engine starts to overheat at idle, or in heavy traffic, and the gauge goes down when you rev it, the coolant is probably low.
Moreover, a neglected cooling system can load up the cap with crud and corrosion, preventing proper coolant flow in and out through it. Peel the seals back with your fingernail to check for goop. If you find any, a blast with a garden hose and probing with a toothpick should clear most of it out.
But anyway, a new rad cap is less than $20. Make a habit to change it every 5 years, just in case. It's pretty important.
--------------------------------------------------------------------------------
Bad thermostat
This part is the traffic cop that controls when the coolant is allowed to circulate and when it isn't. It's the device that's meant to quickly allow the engine to warm up to its design temperature, but no hotter than that.
Thermostats can stick shut or open, get lazy, or fail to open at the correct temperature. Depending on how and when they fail, they will cause either overheating or underheating. Overheating usually happens when the thermostat fails to open, or fails to open enough. If it fails to close, the engine will run too cool, causing all sorts of other problems.
A cooling system full of rust, scale, silt, or gel will interfere with the thermostat's operation, causing even more cooling problems. Gunk can plug up the thermostat, causing overheating, or make it stick open, causing underheating. Incorrect installation of the thermostat (can be done, even by professionals!) will also interfere with thermostat operation.
Normally mounted in the top of the lower rad hose in modern Hondas, the thermostat senses engine heat in the coolant. It is supposed to open up when the coolant in the block has warmed up enough, allow the cooled coolant in the rad to flow into the block, pushing the hot coolant from the block into the rad.
When the thermostat is closed, a small bypass hose allows coolant to circulate through the engine block, around the business end of the thermostat, through the water pump, and back around again. This keeps block temperature even, and helps the thermostat warm up as well. Once the thermostat opens, the bypass is closed off by means of a special extension on the bottom of the thermostat.
Aftermarket thermostats are highly associated with overheating and underheating. Most Hondas require 78C (172F) thermostats (that's the opening temperature). Too many aftermarket thermostats are wrongly rated for your car and are poorly made. Your emissions system may not work correctly with a different rating installed. In addition, some aftermarket units lack a bleed hole, the absence of which can trap air and lead to overheating.
A new genuine Honda thermostat is about $30 and is guaranteed to work properly in your Honda. In my mind, it's foolish to trust such an important job to an aftermarket part. Changing it every 5 years is excellent preventative maintenance.
#6
03-05-2012, 04:25 PM
Judging from how many failed gaskets I've already had to replace, the radiator cap sounds like the best place to start. It looks like most of the parts on this bike haven't been replaced since it was new in 1990, and most are way past usability. I'll order one and see if it helps, as well as adding coolant.
I'll check the radiator for damage too. I haven't ever noticed foam in the reservoir, but I've never been looking for it either. I guess it's back to running without fairings for a bit to watch for these things.
Out of curiosity, how bad is it for the engine when it overheats to the point that it won't run? I'd assume it causes some permanent damage, but it would be nice to know how badly I've messed up the engine over the past week...
Thanks so much for your help! I never would have figured this out reading the service manual.
If anyone else ends up looking through here, I poked through the manual and found that you should fill the radiator with a 50-50 mix of distilled water and ethylene glycol.
I'll check the radiator for damage too. I haven't ever noticed foam in the reservoir, but I've never been looking for it either. I guess it's back to running without fairings for a bit to watch for these things.
Out of curiosity, how bad is it for the engine when it overheats to the point that it won't run? I'd assume it causes some permanent damage, but it would be nice to know how badly I've messed up the engine over the past week...
Thanks so much for your help! I never would have figured this out reading the service manual.
If anyone else ends up looking through here, I poked through the manual and found that you should fill the radiator with a 50-50 mix of distilled water and ethylene glycol.
#8
03-05-2012, 04:32 PM
February 2012 ROTM
1. Fan working, fan sensor working.
2. You have coolant & oil
3. Change radiator cap & thermostat, this insures your coolant is flowing properly. The cap let hot coolant return from engine block when presure is build up to certain psi. The thermostat lets the cooler coolant from the radi to return into the engine block.
Locate your thermostat, should be where the return hose from the radi. Search google to see how parts look like...
How this is the problem and cheap fix...
2. You have coolant & oil
3. Change radiator cap & thermostat, this insures your coolant is flowing properly. The cap let hot coolant return from engine block when presure is build up to certain psi. The thermostat lets the cooler coolant from the radi to return into the engine block.
Locate your thermostat, should be where the return hose from the radi. Search google to see how parts look like...
How this is the problem and cheap fix...
#9
03-05-2012, 04:38 PM
February 2012 ROTM
Don't try starting bike when HOT, it will on further damage to block, i suggest you take it to mechanic and have them do it...
#10
03-05-2012, 05:40 PM
I've done plenty of work on the bike before (rebuilt carbs, new clutch plates, new fork seals) Just because I've never worked on a cooling system doesn't mean I'm mechanically retarded.
I got the thing for $800 a year ago and the list of things that didn't need work is shorter than those that did, but at this point I'm treating it as a learning experience. After all, I'm a college kid, I've got time, but no money. (in retrospect, this makes the purchase a really stupid idea... I've spent way too much on parts) When I graduate, I'll buy a bike 20 years newer and pay someone else to do it. For now, it's up to me.
The thermostat looks simple enough to take out, just two bolts in front of the radiator cap. After mulling it over, I think I'm going to replace both the cap, the thermostat, thermostat gasket, and all the coolant in one go. It's likely only one of them, but I'm sick of pulling the tank off and this will likely save me time down the road. Chances are the coolant is 10+ years old too, and needs to be replaced.
Heh... attempted bump starting it when it was hot... poor block T_T Oh well, I'm going to be selling the thing at a massive loss in 3 months when I leave the island anyway.
I got the thing for $800 a year ago and the list of things that didn't need work is shorter than those that did, but at this point I'm treating it as a learning experience. After all, I'm a college kid, I've got time, but no money. (in retrospect, this makes the purchase a really stupid idea... I've spent way too much on parts) When I graduate, I'll buy a bike 20 years newer and pay someone else to do it. For now, it's up to me.
The thermostat looks simple enough to take out, just two bolts in front of the radiator cap. After mulling it over, I think I'm going to replace both the cap, the thermostat, thermostat gasket, and all the coolant in one go. It's likely only one of them, but I'm sick of pulling the tank off and this will likely save me time down the road. Chances are the coolant is 10+ years old too, and needs to be replaced.
Heh... attempted bump starting it when it was hot... poor block T_T Oh well, I'm going to be selling the thing at a massive loss in 3 months when I leave the island anyway.