88 BII 2.9 Temp fluctuates from 185 to ~215

[BillRod]

Hi All

88 BroncoII 2.9L, Auto, 4x4, A/C, Lots and lots of miles
The temp gauge fluctuates from about 185 to about 215.
Every few minutes it will jump, it only stays at 210 or 215 for a 10 to 15 seconds or so but it does this every 3-5 minutes.
Sometimes it will do it under hard acceleration, other times it will do it just siting still idling.

Here's what I have done so far.
It started with the stock gauge fluctuating.
-Swapped out the thermostat for a Stant brand 195, no change.
-Removed the stock sender unit and installed a Sun mechanical gauge.
-The new mechanical gauge showed the actual temps above.
-Swapped the Stant thermostat for a new Napa 195, again no change.

So I now know I have a more serious problem.

The cooling system is comprised of the thermostat, water pump and radiator.
But I don't want to just start swapping more expensive parts.


Anyone have any thoughts or ideas of things to look at?

Thanks
Bill

 

[piotrsko]

bubbles in the coolant?

more sinister: head or head gasket going bad.

water pump going bad or cavitating.

Ignore #2 if you aren't using any coolant, and park it with the nose way uphill to burp it. while it is cold, pull the radiator cap off while it is running and look for evidence of bubbles.

run a pressure test of the coolant system to see if it is leaking. flush it out, may have a chunk of gunk giving partial blockage.

last case: it could be just a weird thing, 215 ain't all that hot. I'm surprised the gage can react that fast.

 

[jhammel85]

Sounds alot like air in the system.

I would burp it for air 1st....Might as well try the easy cheap stuff 1st right?
Turn it on, remove the cap and let it get close to operating temp. Just make sure not to shut it off with the cap off, it'll suck in air.

If its still doing it, Try another cap. I had a car that did this and it was a bad cap. Bad cap = bad seal = air sucking in system when car is shut off. Its only a few bucks and it wouldnt hurt.

Might want to check the radiator for blockages too. You never know..

 

[BillRod]

Replaced the cap, no change.
No noticable bubbles in the coolant with the cap off.
Both of the themostats I have tried do have the little tiny air vent at the top of it
Not losing any coolant.

No white smoke or evidence of burning coolant.
I changed the oil & filter Saturday when I changed the first thermostat no visual evidence of coolant mixed with the oil.

This weekend I will try to pull the spark plugs to look for more evidence of coolant in the cylinders.
If one or more are very clean then maybe it is sucking in trace amounts of coolant, maybe. I dunno, since there's no other evidence of a head gasket issue, but it would be worth the time to check these.

It seems if it were a radiator blockage it would be much more consistent running hot instead of the way it is bouncing up and down.

Not losing any coolant from the water pump but that's the only thing I can think of maybe the impeller is degraded or starting wobble a little or come loose or something.
They're only $46 at Autozone.
If the plugs look ok this will be my next thing to R&R to inspect.

Anyone have any other thoughts?

Thanks
Bill

 

[Big Jim M]

Leave the sparks alone! Doncha know that if coolant can get into the cylinder then COMPRESSION can get into the radiator? The result of coolant on the sparks is puking and spitting it's coolant out the overflow.
Park on a hill with the radiator higher than the dashboard. With the cap off and the engine running and the heater on high watch the radiator level and FLOW inside the neck. Spend 20 minutes or so all the while filling any needed coolant. If you actually do add coolant then your problem was air in the lines.
Another thing to consider is the temp of the coolant in the radiator. Up there where you live perhaps the coolant is so cold that the thermostat jumps open and then closed. because of the temp change.
Have you put it out on the hiway for a 30 or 40 mile trip to see if the thermostat will find a sweet spot and stay in one opening and the results would be a constant temperature?
Big JIm

 

[country0001]

I've been havin similar problems. I changed thermostat yesterday. It needed it even tho it was only a year old. It did ok for a bit, stayed steady, then it went way hot and stayed hot. I'm thinkin radiator. So today I switched out radiators and put in my 4.0's. It seems to be better, will find out tomorrow.

 

[Epixstar]

my truck does the same thing.it is very cold up here it never drops to much or gets too hot. I always have heat its seems kinda common with these motors.It does sound like air in the system.

 

[BillRod]

Hi All

Still have the issue. But at least I do have a new info.

I tried Big Jim's advice.
I parked in on a burm so that the radiator cap was above the dashboard, let it cool down, pulled the cap turned on the heat and started it back up.

As it warmed up the coolant level started to pulse, it would come up to the neck and barely spill a little out then it would drop a couple of inches then raise up to the neck then drop a couple of inches.
This pulse would rise and fall every 10 - 20 seconds or so.
It continued this pulsing then whole time it was warm running.
Some times spilling some out, sometimes just barly getting to the top of the neck.

This pulsing of the coolant is not in the same rythim as the fluctuation of the temp gauge.
The gauge fluctuates every few minutes, the coolant level with the cap off pulses every 10 - 20 seconds.


1 more small piece of info, just as it got to around where the thermostat would open the engine stumbled for just a second, I noticed this the last couple of times I have started it since this issue arose.


And the temp gauge still fluctuates.
The outside air temp is not that cold here in Colorado Springs as Big Jim asked. I have been trying to diagnose this on days ranging from the mid 30's to almost 50 so the coolant does not start off all that cold.


Any other thoughts anyone?

Thanks
Bill

 

[BillRod]

After doing all that stuff above to burp the system I still had the issue.

I had to borrow a friends truck for the long holiday weekend so I took the Bronco down to leave there.

After driving on the highway a few miles the temp actually started to level off.
When I swapped trucks again after the weekend I continued to drive the Bronco and the temp stayed pretty level but was running warm.

Napa had a 180 degree thermostat so I installed that and now the temp gauge is right where it should be and very consistent.

Sounds like it was apparently an air bubble after all.
I guess all it needed was high rpm highway time to move it.

Thanks all
Bill

 

[Jspafford]

My 89 will run up to 210-215 while sitting idle with the air on. It sounds really hot, but your still safe at those temps as long as you have the proper mix of antifreeze and water.

 

[Big Jim M]

Proper mix doesn't have one damn thing to do with it! ANY water in the mix will still boil at 212* at sea level.. So we put a 16 lb cap on the system. This 16 lbs keeps the WATER in the system from boiling until 240* is reached.
The antifreeze (ethylene glycol) WILL NOT FREEZE until -5*F is reached. Even then it only gets slushy. As far as BOILING ethylene glycol won't boil until it gets to 450*F or thereabouts.
Down here where it hasn't seen -10* in fifty years I run PURE ethylene glycol in my rides. I have NO RUST in the system. It is the water that causes the internal rust and wear on the pump seal.
Big JIm

 

[177CIOfPureLove]

Do not forget to check your fan clutches, when they start to fail they do not cool consistently. Check for oil weeping out of the seal, and for resistance when you spin the fan while the engine is not running. the more the better! I chased problems like you guys had until I realized it was that.

 

[robertc1024]

Down here where it hasn't seen -10* in fifty years I run PURE ethylene glycol in my rides. I have NO RUST in the system. It is the water that causes the internal rust and wear on the pump seal.
Big JIm

There are a couple of issues with running pure ethelyne glycol. First, it's almost 2 times more viscous than water - makes your water pump work harder. Secondly is that it isn't as good as transferring heat as water is. Its specific heat capacity is about 30% less than pure water. I just always make sure the only water that goes into my engine is distilled.

 

[Big Jim M]

Yep!

There are a couple of issues with running pure ethelyne glycol. First, it's almost 2 times more viscous than water - makes your water pump work harder. Secondly is that it isn't as good as transferring heat as water is. Its specific heat capacity is about 30% less than pure water. I just always make sure the only water that goes into my engine is distilled.

That twice as viscous is because it is such a good lubricant. As far as it flowing inside the coolant system it flows as well as any other coolant.

In fact my Bobcat comes from the factory with a german engine and cooling system.. It uses 40W motor oil to cool itself. No problems with freezing there.

Secondly the cooling capacity is more than adequat for an engine. I have used pure ethylene glycol in my vehicles since the 60's. I found out at that time the Arabs were using it in their desert vehicles because it never overheated in the hot desert sun! So being here in Texas I thought maybe it would be a good coolant here if the Arabs were using it there..
Big Jim

 

[Lead Head]

An engine can and still will overheat with pure ethylene glycol. The heads and block will still distort and the headgaskets will blow just the same as if you had a 50/50 60/40 or 70/30 mix. The only difference is that the mixed stuff will boil out, while the ethylene glycol won't. Your engine will still be trashed either way.

Pure ethylene glycol will freeze at 10*F. A 70/30 of ethylene glycol and water respectively will freeze at -60*F.

As it was mentioned pure ethylene glycol does not transfer heat as well as water.