Getting hot at hwy speeds (1 Viewer)

[Meatdawg]

I have read a lot of the other posts about over heating and most seem to apply to getting hot at idle or low speeds. My 1989 FJ62 starts getting hot at highway speeds. It has a 6.0 LS in it for reference and I have run this set up for 12 years now. Here is what I have done so far to try and fix the issue.

1. New Mishimoto aluminum radiator (stock rad had small leaks in it, I did have it repaired and it is in storage, but it had the same symptoms with the stock rad)
2. New Thermostat (187 degree)
3 Running the same electric dual Spal fans since the engine swap. Motor stays cool (200-205 degrees or so at a stop sign in 95 degree weather after driving)
4 Relocated supplemental trans cooler from in front of the radiator to possible improve flow (made no difference)
5 Removed the Warn 8274 (made no difference)
6 Flushed the motor and new radiator, when draining the fluid was pretty clean.
7. Put a spring in the bottom radiator hose to prevent collapse

I have been messing with this for over a year now. One interesting fact is that if I am sitting at idle, fans on and truck at about 200-205 degrees, if I rev the engine to about 2000-2500 RPM the temperature goes down very quickly to around 190. The water pump is stock, but it is not leaking and seems to be functioning as it should.
Around town with stop and go traffic, it usually stays right around 200-205.
In the summer, at 70 MPH (around 2300 RPMs) it will creep up to 240 +. At that point I slow down, turn off the AC and then it cools pretty quickly below about 55 MPH. Hills make it heat up much faster of course.

I do not take the Cruiser on many highway trips, but plan to start getting it out more. I was thinking of maybe just replacing the water pump for kicks. Maybe go with a high flow pump?

Any suggestions or first hand experience would be appreciated, thanks.

 

[FJ Silver]

It kinda sounds like the waterpump is the only thing left..
The fact that when you increase the RPM she cools down quickly could mean the waterpump is maybe rusted out some, or worse if its not a metal pump.

 

[OSS]

I doubt the heating is related to the water pump. A water pump is a direct drive impeller. When a water pump ’fails’ its when the bearing and shaft seal goes and it starts to leak coolant. If the engine is running, the impeller is spinning and coolant is flowing through the engine.

If a radiator is big enough, it will be able to cool any engine at any load. When I was talking to the sales guy at Ron Davis (custom radiators) he mentioned that no electric radiator fan is capable of pumping as much air as a mechanical clutch driven fan. He said to me “don’t let anyone talk you into using an electric radiator fan”.
They sell electric fans for their radiators too.

Your 6.0 is running at the correct temps at idle & loafing because the cooling system can keep up. But when that big engine gets pushed, the heat it’s generating is beyond the capacity of your cooling system to shed.

 

[cps432]

I doubt the heating is related to the water pump. A water pump is a direct drive impeller. When a water pump ’fails’ its when the bearing and shaft seal goes and it starts to leak coolant. If the engine is running, the impeller is spinning and coolant is flowing through the engine.

If a radiator is big enough, it will be able to cool any engine at any load. When I was talking to the sales guy at Ron Davis (custom radiators) he mentioned that no electric radiator fan is capable of pumping as much air as a mechanical clutch driven fan. He said to me “don’t let anyone talk you into using an electric radiator fan”.
They sell electric fans for their radiators too.

Your 6.0 is running at the correct temps at idle & loafing because the cooling system can keep up. But when that big engine gets pushed, the heat it’s generating is beyond the capacity of your cooling system to shed.

But, remember he’s running an LS swap rather than the 2F.

 

[kirvesmies]

But, remember he’s running an LS swap rather than the 2F.

if you read the last sentence OSS wrote, he addressed the 6L

 

[Rgill]

It kinda sounds like the waterpump is the only thing left..
The fact that when you increase the RPM she cools down quickly could mean the waterpump is maybe rusted out some, or worse if its not a metal pump.

I agree check the pump. I have seen more then one pump with missing or corroded impellers. Plastic impellers are the worst for falling apart. Don't remember what the LS pump looks like. If the pump is good then you have restricted flow somewhere. It worked for 12 years so your engineering is good.

 

[Rgill]

if you read the last sentence OSS wrote, he addressed the 6L

So it worked for 12 years and now the system is too small?

 

[kirvesmies]

@Meatdawg , do i understand correctly, the issue started about a year ago? or has it been frustrating you for 12 yrs? if only a year, n nothing has worked, may i suggest a compromised head gasket. yeah, a blown h/g will have obvious signs but a compromised one might not show till you feed the dog n let it hunt.
if 12 years, holy fawk! you're a patient man

 

[kirvesmies]

So it worked for 12 years and now the system is too small?

i are slow some days. trying to figure how long the issue has been rearing it's head

 

[Meatdawg]

@Meatdawg , do i understand correctly, the issue started about a year ago? or has it been frustrating you for 12 yrs? if only a year, n nothing has worked, may i suggest a compromised head gasket. yeah, a blown h/g will have obvious signs but a compromised one might not show till you feed the dog n let it hunt.
if 12 years, holy fawk! you're a patient man

Really just been an issue over the last year or so, but I had not really taken it on any long, Summer road trips for a few years before last Summer.
I will check the head gasket, good call. The oil and coolant look good and I am not losing any coolant, but will look into that.
I am going to go ahead and put in a new water pump as well. Pretty easy job and at least it would rule that out.
Thanks for all the replies everyone, keep them coming if you have any other input.

 

[kirvesmies]

the reason i used 'compromised' was a good friend of mine is an engine builder and one of his bullets in a respectably quick pro/st car had exactly the same symptoms you described. took tearing the engine down to find it, the combustion chamber edge just looked a little different right by a water jacket port. swap gasket, button back up n run it, problem gone. hope you get it sorted

 

[OSS]

I’ll say that in my younger foolish years, I changed my coolant (which was always green coolant) with the “new fancy” orange dexcool coolant. I didn’t completely flush the engine before adding the orange stuff- just drained & refilled.

Years later my engine started running hot and nothing I could figure was causing it. Eventually I removed the cylinder head and -Low & Behold- all the little coolant holes in the head gasket were clogged up with a jelly type goo — Dexcool precipitate.

That coolant mixed with the green stuff creates jelly inside the engine which clogs small coolant passageways.
There’s a reason that orange coolant got its well deserved nickname — Deathcool.