Random Overheating
06-17-2003, 12:11 AM
#1
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Join Date: Jun 2003
Posts: 2
Random Overheating
Hi all,
I've been a lurker here for a while. Registered now I need to post a Q that searching hasn't fixed.
I have a June 1990 built in Japan Australian Maxima Ti. I love my Max even tho it costs an arm and a leg to keep running. It has climate control, velour trim and all the Ti usuals. For it's age and 300,000Km (about 180,000miles) it is a great family truckster
It has a funny habit of overheating at random, usually about 30-60 minutes into a drive. So far I've had the radiator pulled and cleaned. It was 20% blocked but is now 100% clean. I replaced the thermostat (old one tested OK, but replaced it anyway). I've also replaced the radiator cap in case it was losing pressure there. There are no water losses until it overheats and vents thru the overflow tank. I've had the cooling system pressure tested and it holds perfectly. Just this weird random overheat.
What we've noticed is that if we leave the cap off until it warms up, water seems to spurt through to the rad rather than flow - ie it's like the motor is really cooking the water. I ended up removing the thermostat altogether and just let it run free-flowing. This reduced the frequency of the problem but it still pops up occassionally. It also got a new top hose as I cracked the old one doing all those thermostat removes and replaces
I've had the coolant tested for CO in case of a faulty head gasket but test returned negative. There are no traces of coolant in the oil. I pressurised the cooling system with the engine warm then cranked the engine with the spark plugs removed and there is no water coming out of the plugs. Thermo fans are OK.
It seems to be able to idle for hours on end and is OK so long as there is no load on the motor. If it's idled in Drive, tho, it overheats sooner. There is nothing weird in the shifting tho. The transmission was rebuilt last year by an automatic specialist and the tranny fluid colour is right, no signs or scent of burning there.
What else can I test? Possibly the auto tranny cooler?
Has anyone seen anything like it before? It has both my mechanic and myself completely stumped.
I've been a lurker here for a while. Registered now I need to post a Q that searching hasn't fixed.
I have a June 1990 built in Japan Australian Maxima Ti. I love my Max even tho it costs an arm and a leg to keep running. It has climate control, velour trim and all the Ti usuals. For it's age and 300,000Km (about 180,000miles) it is a great family truckster
It has a funny habit of overheating at random, usually about 30-60 minutes into a drive. So far I've had the radiator pulled and cleaned. It was 20% blocked but is now 100% clean. I replaced the thermostat (old one tested OK, but replaced it anyway). I've also replaced the radiator cap in case it was losing pressure there. There are no water losses until it overheats and vents thru the overflow tank. I've had the cooling system pressure tested and it holds perfectly. Just this weird random overheat.
What we've noticed is that if we leave the cap off until it warms up, water seems to spurt through to the rad rather than flow - ie it's like the motor is really cooking the water. I ended up removing the thermostat altogether and just let it run free-flowing. This reduced the frequency of the problem but it still pops up occassionally. It also got a new top hose as I cracked the old one doing all those thermostat removes and replaces
I've had the coolant tested for CO in case of a faulty head gasket but test returned negative. There are no traces of coolant in the oil. I pressurised the cooling system with the engine warm then cranked the engine with the spark plugs removed and there is no water coming out of the plugs. Thermo fans are OK.
It seems to be able to idle for hours on end and is OK so long as there is no load on the motor. If it's idled in Drive, tho, it overheats sooner. There is nothing weird in the shifting tho. The transmission was rebuilt last year by an automatic specialist and the tranny fluid colour is right, no signs or scent of burning there.
What else can I test? Possibly the auto tranny cooler?
Has anyone seen anything like it before? It has both my mechanic and myself completely stumped.
06-17-2003, 05:33 AM
#2
Member who somehow became The President of The SE-L Club
iTrader: (19)
Join Date: Jun 2001
Posts: 16,033
Make sure your thermostat isn't in backwards.
A backwards thermostat will be opening against fluid flow. When the engine is really hot, the spring is very lose and the water flow may actually be pushing it closed and reducing the flow.
A backwards thermostat will be opening against fluid flow. When the engine is really hot, the spring is very lose and the water flow may actually be pushing it closed and reducing the flow.
06-17-2003, 09:26 AM
#4
U wanna try me young boy?
Join Date: May 2001
Posts: 1,024
You didn't mention replacing the water pump...
30-60 is a weird time to begin to overheat... The engine is going to getup to normal operating temp in like 5 mins ('specially in oz).
The troubleshooting steps you've taken so far are pretty indepth - I'm surprised you still have a problem that you haven't found. You could try turning the heater on when it overheats and see if that helps bring the temp down.
What is the typical ambient temperature where you live?
I'd prolly even try a bigger radiator.
Also I'd consider installing an auxilliary trans cooler and stop using the trans cooler in that's built into the rad - you don't want your overheating to heat up the trans fluid, and you don't want the hot trans fluid making your rad work harder.
30-60 is a weird time to begin to overheat... The engine is going to getup to normal operating temp in like 5 mins ('specially in oz).
The troubleshooting steps you've taken so far are pretty indepth - I'm surprised you still have a problem that you haven't found. You could try turning the heater on when it overheats and see if that helps bring the temp down.
What is the typical ambient temperature where you live?
I'd prolly even try a bigger radiator.
Also I'd consider installing an auxilliary trans cooler and stop using the trans cooler in that's built into the rad - you don't want your overheating to heat up the trans fluid, and you don't want the hot trans fluid making your rad work harder.
06-17-2003, 01:52 PM
#6
Supporting Maxima.org Member
Join Date: Aug 2002
Posts: 488
Originally posted by tecman4
I would look at the water pump,
also try running your heat on high and hot, that will cool your engine a little more
I would look at the water pump,
also try running your heat on high and hot, that will cool your engine a little more
06-17-2003, 07:55 PM
#7
Newbie - Just Registered
Thread Starter
Join Date: Jun 2003
Posts: 2
To those who've offerred advice so far, my thanks.
Answering questions:
It's winter here now and ambient is about 20°C 68°F, I suppose. Keeps well above freezing at night.
The thermostat is presently out altogether, so it's not that.
I use the heater on trick to cool a little more, but when the problem happens... nothing like a few extra sq metres of fins is going to help.
I was planning on an aux transmission cooler, but given the age and value of the car, I sort of passed up the idea.
How can I check the water pump without removing it from the car? My mechanic quoted 5 hours' labour to R&R it for a check. I don't want to throw more money at this than I have to and I don't want to R&R the pump myself... if I can avoid it.
I ran a garden hose in thru the bottom hose with mains pressure the last time I changed the thermostat and water came pouring out the front of the block, as I imagined it should... Doesn't guarantee that the whole block is clear tho...
Answering questions:
It's winter here now and ambient is about 20°C 68°F, I suppose. Keeps well above freezing at night.
The thermostat is presently out altogether, so it's not that.
I use the heater on trick to cool a little more, but when the problem happens... nothing like a few extra sq metres of fins is going to help.
I was planning on an aux transmission cooler, but given the age and value of the car, I sort of passed up the idea.
How can I check the water pump without removing it from the car? My mechanic quoted 5 hours' labour to R&R it for a check. I don't want to throw more money at this than I have to and I don't want to R&R the pump myself... if I can avoid it.
I ran a garden hose in thru the bottom hose with mains pressure the last time I changed the thermostat and water came pouring out the front of the block, as I imagined it should... Doesn't guarantee that the whole block is clear tho...
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