Forum:
I've just done the head gasket on my 92 sportrak, it was bubbling in the expansion tank and overheating, had the head skimmed and fitted a new thermostat.The problem is that it is running approx 3/4 across the temp gauge not boiling mind. The top of the rad is really hot and the bottom is clap cold which would suggest the water isn't cirulating.I've had both the old stat and the new one in boiling water and they both open and they are the long ones with the curved plate on the end.It does the same thing with either fitted. I ran it without a stat and you could see the water flow across the top of the rad with the cap off which would suggest that the pump is ok and the rad isn't blocked, water comes out the bottom as fast as you can tip in the top.
Anyone come across similar problems.
It could be that the cross
It could be that the cross tubes are blocked, or partially blocked, these are crossflow type radiators so water movs from one side to the other through all or some of the tubes.
If some are blocked it will feel cold in these areas, back flush the radiator and clean the cooling system.
Look in the "How It Works" section, i have written an article on cleaning the cooling system.
Also check for air locks as
Also check for air locks as these will inhibit flow and reduce the cooling water from the cooling system as they fill.
Cross tubes?
The cooling tubes in this rad are vertical and water flows readily through them. I continually sqeeze the bottom hose when filling to eliminate air locks. The bottom hose does warm slightly after you stop the engine but I suspect this is hot water percollating through the small hole with the joggle pin in the stat.
Jiggle.
Did you fit the thermostat correctly? The jiggle [the hole in the thermostat plate] must be uppermost. If incorrect the air will not escape into the cylinder and the thermostat will not open because the wax-spring is surrounded by warm air and not hot coolant.
TIP .... take it gently when tightening the housing and use sealant. Those nuts snap at 5 lb/inch.
Temp gauge 3/4 could be OK. Previously it might have been running with a dodgy/old thermostat fully open.
Cross flow radiators come in
Cross flow radiators come in two types, they can have the tubes veritcal or horizontal.
Check the coolant is hot at the top, if the bottom is cold then it is usually a problem with the radiator. If the top is hot and the bottom is slightly warm, ir warmer much cooler than the top the radiator is doing its job of efficiently cooling.
Radiator problems are those of blockages, not necessarily those with debris physically blocking the tubes, it can be scale formed or forming inside the tubes. This inhibits the cooling capability of the radiator, also the wrong radiator may be fitted as some are model specific.
Fitting the thermostat correctly is a must, they can create air locks and not work effectively.
Water pumps may appear to be working correctly, but if the blades on the impellor are deteriorated they may not move as much water as they should. Check the water pump, one other problem i have encountered is the wrong size pulley being fitted to the water pump. This means it is rotating too slowly and not moving enough water, compare pulleys with an identical model to your own.
If the engine block has scale formed inside it, it will not allow the water to remove heat from the engine as quickly as it should.
Sorted this one. On sunday
Sorted this one. On sunday rebuilt motor with new stat, overheated. On Mon night fitted old stat overheated after a longish run found small leak on bypass hose, clip not tight enough. Tues night fixed leak refitted new stat overheated again. Wed night took out new stat and closely compared it with old one found the curved plate on the end of the stat was 90 degrees round from the old one, refitted old stat had a fast run up and down the dual carriageway ran dead on normal, problem solved.
Moral of the story? Don't buy sportrak thermostats from motor factors get a genuine one.
Thanks for all the help and advice.