3B fluctuating coolant temps. Any ideas? (1 Viewer)

[TysonFunk]

I have an 84 BJ60 3B turbo 385k km (non intercooled, 9lbs, original head gasket)
I replaced the entire cooling system 3 years ago, (4 core rad, water pump, t-stat, rad cap, hoses etc)
It has an auxiliary coolant temp gauge and when I let the truck idle for a bit, after its reached operating temperature, I've noticed the coolant temp needle drops down to zero on both the factory and auxiliary gauge. When I start driving, it remains at zero for a minute or so and then jumps back up to operating temperature.

My heater seems to pump warm, not hot air when the truck is at operating temp (82 degrees C)

I've noticed that after I shut down the engine, my overflow tank bubbles for a few seconds as if there's an excess amount of pressure in my cooling system.

No overheating issues luckily

Any ideas as to what this could be? air bubble in the coolant system? blown head gasket?

Thanks in advance!

 

[OTBT]

I think that your coolant level is low. The reason I think this is because when the engine starts from cold, the thermostat is closed, therefore bypassing the radiator, but as the engine warms up to operating temp, the thermostat opens and cold coolant is pumped into the system, therefore closing the thermostat again until that coolant gets warm enough to open it again ... and so the cycle continues until everything is nice and toasty. When the thermostat is open and the entire cooling system operates as it should, the engine temp should remain fairly constant. If, your coolant level is low enough so as to not cover the temp sensor near the thermostat, the engine temp will read zero.

I have found with my 3B and other B's before it, I need to burp my system quite a bit when adding coolant in order to get the coolant level to fill the block, oil cooler, head, heater, hoses, radiator and expansion tank. I do this by squeezing the return hose repeatedly when the engine is warm.

Having said all this, if your sensors are not where I think they are, then I may be way out to lunch.

I hope this helps, Glenn

 

[TysonFunk]

I think that your coolant level is low. The reason I think this is because when the engine starts from cold, the thermostat is closed, therefore bypassing the radiator, but as the engine warms up to operating temp, the thermostat opens and cold coolant is pumped into the system, therefore closing the thermostat again until that coolant gets warm enough to open it again ... and so the cycle continues until everything is nice and toasty. When the thermostat is open and the entire cooling system operates as it should, the engine temp should remain fairly constant. If, your coolant level is low enough so as to not cover the temp sensor near the thermostat, the engine temp will read zero.

I have found with my 3B and other B's before it, I need to burp my system quite a bit when adding coolant in order to get the coolant level to fill the block, oil cooler, head, heater, hoses, radiator and expansion tank. I do this by squeezing the return hose repeatedly when the engine is warm.

Having said all this, if your sensors are not where I think they are, then I may be way out to lunch.

I hope this helps, Glenn

So I went and got a coolant flush from a local shop. They burped the system and it seems to still be eating coolant / bubbling in the overflow at shutoff. I’m now thinking that my head gasket is blown or worse, the head is cracked and letting combustion gasses into the cooling system / burning coolant. I’ve notice the engine sputters a bit on warm start ups and the exhaust puffs white smoke that smells a bit sweet as if coolant is leaking into one of the cylinders and burning off quickly at start up causing the engine to sputter for a second. That’s only a guess however. I’ve yet to order a combustion gas tester and see for sure but as of now that is my only prognosis.

 

[bj70bc]

hey, where are you in bc?
when i botched my MLS head gasket install that is what would occur (bubling in the overflow) minus the 0 readings on the gauges.
I did my HG as preventative maintenance
are you still getting 0 readings after the flush refill and burping?
Original composite gaskets wont hold up to boost for too long....if original its probably toast.
And unfortunately even if it is 'just' the head gasket the head is most certainly cracked between the valves, they all are (very high probability) mine was in 2 places.
The cracks might not be letting combustion gasses through but they could and eventually will, and if your taking the head off you should address that.
At the very least your precups WILL be cracked so plan to do those for sure if the head comes off, radd cruisers has em at a good price.
As ive gone through this recently just ask if there is anything i can help with.

FYI buy the toyota head gasket dont get the aftermarket...its too thin to seal properly

 

[TysonFunk]

hey, where are you in bc?
when i botched my MLS head gasket install that is what would occur (bubling in the overflow) minus the 0 readings on the gauges.
I did my HG as preventative maintenance
are you still getting 0 readings after the flush refill and burping?
Original composite gaskets wont hold up to boost for too long....if original its probably toast.
And unfortunately even if it is 'just' the head gasket the head is most certainly cracked between the valves, they all are (very high probability) mine was in 2 places.
The cracks might not be letting combustion gasses through but they could and eventually will, and if your taking the head off you should address that.
At the very least your precups WILL be cracked so plan to do those for sure if the head comes off, radd cruisers has em at a good price.
As ive gone through this recently just ask if there is anything i can help with.

FYI buy the toyota head gasket dont get the aftermarket...its too thin to seal properly

Im up in squamish. Getting an accurate reading on the gauge now but definitely burning through a fair bit of coolant (between bubbling out and probably consumption)

Thanks for the info! I definitely knew a HG replacement would be sometime in the near future after I installed the turbo. I preemptively ordered a OEM head gasket from Toyota and pre cups to replace the original and was planning to tear into it a little sooner but the moment, it’s currently my daily. So until I can buy another vehicle I might just have to limit my driving. Although it hasn’t been overheating I’m sure it’s not good for the cylinders to take in coolant for an extended period of time.

 

[bj70bc]

im up in PG
yes it will start hurting other things....
i wouldnt do it, might do something to your rings etc, then its a total teardown instead of just a headgasket.
it is possible to do a headgasket in a weekend.... just sayin
i found the start of corrosion on the valves from just running it twice sucking in coolant.
if you were closer id give you a hand doin it....