erratic overheating

[007]

if compression is leaking from the head gasket to the water jacket, you should be able to see tiny bubbles with the engine running and radiator cap taken off. going by the symptoms you describe, I have a strong suspicion it is your fan relay and / or thermoswitch [2 pin thing sticking out of the thermostat housing] that is / are faulty. just because a relay checks out once or twice does not rule out the possibility of it failing to engage intermittently. I suggest you change the relay and if available, thermoswitch before you go about yanking the head off.

[pardizzle21]

hi, if the thermoswitch is the sensor going into the thermostat iv already replaced it, no change.
The fan comes on fine, ie when you let it sit on drive warming up then fan will kick in.but when car is fully overheating sometimes the fans are ON yet the temp doesnt go down, which i why i suspect it to be a different problem.
Its doing my head in, got 3 things left to do.
1-finally wire up a permenant fanswitch
2-replace waterpump(done 112,000 miles)
3-head inspection +new gasket

bloody carrrrrr

[007]

if you say the fans are on and yet the temp is on the rise, then wiring up a direct fan switch will not solve the issue.

try the bubble test to see if the head gasket is leaky. if possible a compression and / or leakdown test too.

finally, next time it overheats, try turning the cabin heater on full blast and see if that brings your coolant temperature down. what you are essentially doing is bypassing the regular radiator circuit and radiating inside the cabin. if it gets your temps down, then your problem is circulation related.

[pardizzle21]

hi, thanks for the replies.
sometimes when the car is overheating the fans are not on, yet sometimes during overheating they are on?! which is why i thought il try a permenant wire up to the fan to see if this resolves anything.


Upon checking the coolant tank it does appear a little bubbly during overheating-dunno if this is evidence of head gasket failure?

Its erratic, but id say on average when i put the fans full blast it doesnt make much/if any difference.
Sometimes the best way i have to cool it is by taking my foot off the gas!

thanks

[hondamake]

If it is overheating and the fans sometimes do/don't come on I strongly suggest that you go back to my earlier post about air pockets in the coolant circuit. When the temp sensor is in overheated water it shows on the dash temp gauge as too hot. When there is no water near the sensor it will give an artificially low reading. When I owned a number of trucks I lost some very expensive engines due to driver ignorance, the post mortem usually went: "I was cruising at 60 mph and the temp gauge went off the scale but after another 10 miles it came back down again, I thought everything was OK then the engine seized!" Usually it was either a fan belt or a sudden water loss due to hose/radiator/gasket failure. The point being once there is no water at the temp sensor it will try to tell you that everything is A.O.K.

[007]

compression / leakdown test should be your first order of business. it is always advisable to perform proper diagnosis before deciding to replace / dismantle anything. it would really suck if you changed your water pump or took the head off and replaced it and the problem still persisted because the cause is something else.

head gasket issues will typically manifest themselves in the following ways:
1. tiny bubbles in the coolant when you rev the engine steadily at idle with the radiator cap off.
2. moss like gunk sticking to the radiator cap.
3. high pressure in the radiator even when the system is cold. opening the cap will let out an unmistakable puff of air.
4. lot of coolant being pushed into the overflow canister.
5. dark / dirty looking coolant.

I don't remember reading before, but did you also replace the thermostat valve [not switch] with a new one? a bad thermostat valve is a very common reason for such issues. if you can replicate your overheating consistently, you may want to try doing the same thing with the thermostat valve temporarily taken out. this will cause the coolant to circulate always. if that solves your heating issues, then you know that you need a new valve.

[pardizzle21]

hi,
regarding air pockets steve, would this not of been resolved when i got the coolant system bled?If not how can i fix?

007-- By thermostat valve what do you mean?the actual stat itself?because iv changed that too.
The water pump has never been changed, so im gonna change it regardless.

[pardizzle21]

Quick one 007

"lots of coolant being pushed into the overflow" iv noticed this before.when car is cold the water ;level is within the min and max, but when hot hot it is nearly full.is this a sign of headgasket??

thanks for help everyone

[007]

yes Pardoe. I mean the actual thermostat. did you use an OEM thermostat or a replacement one? it is not uncommon for a replacement to be faulty right out of the box.

when the engine is hot, it is normal for some coolant to be pushed into the overflow. that is what the container is meant for. when the temps are high and pressure is high [because of the pump working at high RPM], the system pressure increases and when it exceeds the rating of your radiator cap, the relief spring opens and lets the pressure drop to safe levels. once the engine cools down, the coolant contracts and a vacuum is created. this vacuum sucks the overflown coolant back into the radiator.

if your overflow container is not being overwhelmed, I would say you are alright. there could still be a chance that compression leaking from the head gasket could be causing a pressure buildup and making the coolant overflow.

[hondamake]

Hi Tom. The air, more correctly fuel/exhaust/air vapour, pockets I described are not there and stuck waiting to be bled out. They are constantly re-created by pressure leakage from a cylinder(s). Everything is hunky dory one minute then suddenly the temp gauge goes off the scale. You stop the car wait for it to cool and check the coolant, the level is fine and there is no other obvious problem. You start the car again and everything is fine, possibly for days, but then the problem re-occurs. Sound familiar? If this is the problem and goes undiagnosed eventually a hose or the radiator will burst. I used to get this problem with high mileage cast block diesels, the "land" in the bore above the travel of the top piston ring would become porous giving all the above symptoms usually initially diagnosed as gasket failure. PM me your mobi number if you want chapter and verse.