Why does my engine overheat when I stop???

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By The Pink Bitch:

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(This originally posted on Oldholden.com 01.06.2005 in response to question about a red six with stock radiator & 16 inch thermo fan overheating when stopped in traffic.)


If it's been more than a month or so since you last had your radiator "rod cleaned" it may be blocked. You can get an idea of the condition of the tubes by opening the radiator cap, draining out some coolant, and inspecting the tops of the tubes you can see. Of course you can't see most of them, and you can't see ANY of the bottoms of the tubes, OR the insides. The only way to be sure is to pull your radiator out of the car, have a radiator joint take off the top and bottom tanks, clean each tube individually, and solder the top & bottom tanks back on. This should cost around $100 if you remove and refit the radiator yourself. The last time I had this done, it had only been a year since the previous "Rod Clean" and it looked fine from the top, yet when disassembled and flow tested, proved to be 30% blocked.

(a) While you have your radiator out, get the radiator joint to do a cooling system backflush at the same time. This is highly advisable, as it will get out some gunk which is otherwise just gonna clog up your radiator again. You can flush out your radiator at home, but using a garden hose will not yield the same results as a high pressure back flush at a radiator shop.
(b) USE COOLANT. It will prevent any more rust and corrosion from causing little rust flakes in your cooling system. DO NOT MIX DIFFERENT TYPES OF COOLANT, they don't necessarily react too well together.
(c) Fit a top hose filter. You can make your own with a piece of mesh jammed into your top hose, or you can buy them for around $50 (with screw lid for easy access) These can be cleaned easily, as often as you like, and stop anything bigger than about 1mm getting into your radiator.

CHECK YOUR WATER PUMP IS OK. Clearance between impeller and body for a red six should be 0.2 - 0.9 mm. Obvious rust and pitting means it's u/s.

THERMATIC FANS If you don't have one, they can help. Make sure your thermo fan is mounted on the front of your radiator, it has a shroud, and it is blowing air from FRONT to BACK. When sourcing a thermatic fan, ask how many CFM (Cubic Feet per minute) it is good for. You can get fans with curved blades which have a MUCH higher air flow rate than the flat bladed type, you might want to try one of these.
THERMO FANS ON THE BACK OF THE RADIATOR. If you have to / want to fit an electric fan between radiator and engine, make sure you remove the impeller and put it back on backwards (they are designed to push, not suck). Then wire it up positive to negative to make it run the other way.

MECHANICAL FANS If you have removed the fan, consider refitting a mechanical radiator fan. this will help as it will make more air flow around the engine as well as throught the radiator. This cools the engine directly and is far more effective than a thermatic fan alone.

ELECTRIC WATER PUMPS Consider fitting a Craig Davies electric water pump. see ReaperHR's members shed for details of how to fit. $300 or so and should help improve cooling. Will make the water flow faster at idle. These can be used in conjunction with the existing mechanical water pump, or you can remove the mechanical water pump and thermostat and run the EWP on it's own. Fitting an EWP is good for your engine anyhow (it stops the engine overheating once you turn it off, cause the water is still circulating.)

BIGGER RADIATORS For a six, fit a 3 core radiator. I have a 3 core that is only about 5 mm thicker than a stock radiator on my warm 202. It makes a huge difference.

OIL COOLERS Consider fitting an oil cooler. (helps lower engine temp.) About $200 will buy you one brand new. These are also beneficial to your engine as they increase oil viscosity as well as assisting with engine cooling. More importantly, they (obviously) keep oil temperature down, and oil overtemperature is one of the main causes of oil deterioration and "breakdown".

DOUBLE BAFFLE, TRIPLE BYPASS RADIATORS You might like to try fitting a "double baffle, triple bypass" setup on your radiator. Call AUSSIE DESERT COOLERS (VIC) or NATRAD ARMADALE (WA) for information on what this is and how it helps. I have one and it is the bees knees. Essentially it forces the water to go through your radiator 3 times instead of once. Note:if the engine has a wild cam and has a high idle speed as a result, cooling the engine can be a problem. Extra cores, fans and air velocityis likely to be needed to dissipate the extra heat from the extra revs.


See alos Overheating



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