odd things are happening with my engine temps

1396midget

1396midget

Well-Known Member
Evening all.

Anyone got any thoughts on the following?

Car appears to overheat when driving at motorway speeds. It's started recently, the first symptoms were odd: it would climb the temp gauge after slowing down, all the way up to about 110 C, then would go back to normal.

For this I diagnosed a sticky thermostat, so swapped it out.

Now it runs hot ( right up into the red) on the gauge when going over 60. When stopped, it then will return to normal with the twin electric fans switched on.

It has a new water pump, new stat, heater works, there is flow from carb tower, and I'm running an expansion tank and filled it through the heater hose. The fuel gauge stays where it should be throughout.

It's started doing this since the rebuild on the front end, which involved a new pump etc. The water pump is a short nose type, originally destined for an mgbv8.

Current thoughts are to richen it up a bit, or take some advance off. It doesn't pink, and it doesn't overheat under idle conditions either. Could it be that the water pump is pushing it through the rad too fast at higher speeds?

Any other views most appreciated!
 
could this be the water pump failing? when the revs drop it's not getting enough coolant through to dissipate the heat?
 
things go wrong when they're brand new or old in my experience... so it is still in the danger period?
 
Shouldn't be, it's only done about 250 miles on it! Always a possibility though I suppose.

Have had a thought that it might be a slackish fan belt, but can't open the bonnet cos it's in the garage backwards having a rear brake adjusting session...
 
Overheating at high speeds (engine and road) is normally a sign of a blocked radiator. Take it for a run and when it's nice and hot turn the engine off and feel for cold spots in the matrix.
 
Will try that tomorrow. Do they just block? Had it sat empty for a bit so maybe it's upset itself. Coolant isn't nasty or anything...
 
1396midget wrote,...
Do they just block?
Click to expand...

Hi Rob,

Either one of two ways. Sediment collects within the tubes leading to insufficient coolant flow through the radiator, thus at highway speeds, the engine will run hot. The second option is that the air flow through the fins that link the tubes is in someway compromised, either through damage or insect collection.

The only way that the water pump would be moving the coolant at a rate greater than necessary in order to dissipate heat through the radiator, would be if the pulley on either the pump or the crankshaft was the incorrect size.

When the gauge is showing the needle sitting over the 8 and again when it is close to or in the red, how hard is the top radiator hose? Does it feel solid or soft?

Ron.
 
If you think its blocked,drain it out,block the bottom hole up and fill it with cheap cola and let it sit overnight,then flush it out,alternate from top and bottom!
Or you could use kettle descaler and leave overnight!
 
Pilkie said:
If you think its blocked,drain it out,block the bottom hole up and fill it with cheap cola and let it sit overnight,then flush it out,alternate from top and bottom!
Or you could use kettle descaler and leave overnight!
Click to expand...
Half and half white vinegar and water, run it up to temp and let it idle for half an hour then drain and flush a few times.
Worked on my old Honda, cleaned the core to the point where the crud unblocked all the pinholes, needing a new core..... :shock:
 
Been doing a bit of investigating and I've got decent flow from the carb tower, the rad feels normal (hot at top, cold at bottom), the top hose is squashy and the bottom hose more so when running. I've tightened the fan belt, retarded it a bit and richened it up, but going to take rad off and flush when I get a chance. Got its MOT tomorrow, so will sort that first!
 
Top hose should be hard at temp, with the stat open. The system works at 15 psi which is double most cars. Have you got the right rad cap?
 
MOT passed (yay!) temperature still strange. Will be doing a full system flush next, see if that mends it. Have got the right rad cap, nothing has changed except water pump. Might still have air in it, or heater matrix blocked, or the gauge has gone funny, or something else! Still, keeps me off the streets at night...
 
Rob, does it exhibit the same symptoms when stationary revving to motorway revs?
New pump pulley alignment ok?
Do you think your belt could be slipping? Or since it's the only major change and it's a new unknown part, perhaps the water pump pulley is actually slipping on the shaft? Not sure how realistic that is though :?
You could mark the shaft and nose to see if it changes..
Jim
 
thanks all!

one of the things is that it took me ages to mend the water pump sheared bolt, meaning the car stood with no coolant in it and the radiator empty for about 4 months :( entirely possible that something's got upset after that.

The last think i touched was the temperature sender...

I'll check the pump thing. Should be behaving itself..... Belt's nice and tight though. I'll have to try revving it up without going anywhere too, at least it sounds good!
 
For all intents and purposes, all the pump does is move the water through the system, and if it's coming out the carb tower and the water is moving then the culprit is most likely the radiator. As you say, it stood dry for a while, so chances are what was in suspension could have dried out and clogged up the works somewhat.
 
Is this not a job for an infra red thermometer so that you can independently verify the engine and radiator temps?
 
afternoon all

Did a huge flush out with the hose; backwards and forwards. Heater matrix seemed to contain some gunge but flushed out OK. Radiator had some manky brown stuff in but ran clear reasonably soon. Not sure the hose had enough flow to clean it out properly, the pipes on the rad are very big...

There are more clues - the radiator top hose is hot, and feels hard; not completely un-squeezeable but definitely harder than when it's not running. How hard is is supposed to be? Presumably at least 15psi if the cap is working properly. The bottom hose is the same hardness, as are the two heater pipes. These stay hard for a bit after it's shut off.

There is a small hole in the top of the rad, where the side tank joins on, which is making a small steamy steam; meant I had to go on the train rather than drive it for 2 hours....

Coolant isn't manky, oil isn't manky.... It idles fine, has plenty of power and doesn't pink at all.

Need to get a new rad, or have that one mended, anything else to check? I need to renew the heater hoses as one has small cracks on the outside (but doesn't leak) (they were new ones but haven't lasted that well)
 
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