Thread: Temperature spikes in 4BD1T

Last time I was looking, I couldn't even find a non-genuine thermostat.

I'd go there first.

sounds like a thermostat to me, just because they are new dont mean they work okay..

Rijidij

I would look at getting a genuine thermostat form Isuzu - I paid something like $65.00 for thermostat and "O" ring. My 4BD1T tends to spike a bit in water temp on big hills and then gradually recovers - it could be that the thermostat is not fully open when the load comes on the engine which causes the spike in water temp - see my post on water temps - I have been thinking of fitting a larger radiator.

Christopher

Murray,

I would definately go with the new genuine thermostat. Mine was sticking open, as I went down hills the temp would drop right off. When I replaced it, it still had the 1988 date stamp on it
That means it had travelled 500,000+km.

Anyhow,the new one is fine now, with my 3 row RRC radiator, it sits exactly half, even with towing and the A/C on etc.

JC

Thanks guys,
Like I said I should have listened to my mate who told me to " Make sure you fit a genuine thermo".
A member on here has generously offered me a spare brand new thermo. It will be interesting to see if it makes the difference.
It's so easy to fit a new thermo, it would be the first thing I try, but I thought I would pose the question just in case there had been any other issues with spiking.
I had the V8 in the County for 13 years and whenever I had any hint of temp problems it was always the thermo.

Cheers, Murray

Took the County for a run today with a new genuine thermo fitted. It was only about a 50km trip, but all seems well so far. Probably need a longer, warmer drive to really test it out. The temp seemed more stable with the new thermo though.
Visibly, the genuine thermo looks to be better quality than the non-gen one.
Hopefully it's the end of the problem.

I've had the Genuine thermo in for quite some time now and it has been much better, but it still spikes now and then. Most noticably, when I'm travelling at 100 kph it's all good, then I slow down to go through a small town and the temp will suddenly spike up to 100*. It only stays there for 10 or 20 seconds, then slowly goes back to 82* where it's supposed to be. It's also no problem while 4WDing in the bush at high or low RPM, even when working it hard up long steep hills. It never actually 'overheats'.
I noticed it's losing water out the overflow hose from the pressure cap. On the trip we just did, 2 mornings in a row I put approximately 1.5 litres in to top it up.
The rad cap is stamped with the numbers 16 and 110.......is this the correct cap ? It was a new one I got when I had the V8 in and still appears to be in good condition. Is the Isuzu supposed to have a different cap ?

Cheers, Murray

Based on the symptoms, I'd say its likely to be a faulty pressure cap (i.e. it's not holding pressure)

If you're losing coolant through the cap, either its not holding to its rated pressure, or you have air in the system.

If its a V8 cap, it's rated to 16 psi. At this pressure, the boiling point of water is 121 degrees. If it didn't exceed 121 degrees, the pressurised coolant shouldn't boil (and there shouldn't be any loss).

Alternatively, if the pressure cap doesn't hold ANY pressure, the coolant would start boiling at exactly 100 degrees, so the temperature would reach 100*C and then stay there while the coolant is boiling (explaining your coolant loss). If its holding some pressure it would go past 100*C, and how much past would depend on how much pressure the cap is holding.

If your pressure cap tests OK, I would look for a split in the coolant reservoir, or a leak elsewhere in the system - (it would have to be one of the higher points in the system).

I wouldn't worry about the temperature spiking for a short time after slowing down from 100km/h, especially if the system isn't holing pressure. => At high load the engine is producing plenty of heat, but at that speed, the airflow over the radiator gives it enough capacity to dissipate it. As the car slows down, the radiator has instantly lost some of its ability to transfer heat, while there's is heat temporarily stored in the engine block even after the engine stops producing it. The coolant temperature increases to a new equilibirum point until the heat stored in the block is dissipated, after which it goes back to normal temp as determined by the thermostat.

It fits, I just hope its that simple.

Cheers

Bojan