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240 Intermittent Cooling Issues

crscx1

crscx1

New member
Joined
Mar 26, 2019
Location
New York
Hey, Apologies if this is a repeat but I'm relatively new here and this forum isn't the easiest to navigate.

Basically on longer stretches of highway at 65-80mph the temp gauge creeps to a little more than 3/4 of the way up. It has never touched the red and stays right about there. It will drop right back down to operating temperature after I blast the heat for a minute and will stay down for a while before creeping back up. It is also worth noting that this does not happen at all while city driving, or even very spirited driving, only for longer stretches on the highway.

About a year ago I installed an IPD vx cam and did a coolant flush with a new water pump at the same time, This is when the issues began to occur. Very recently I installed a new thermostat which had no effect on the issue.

My thought was maybe in the process of draining the coolant and installing water pump I freed up some 20 y/o crud and there is now a blockage in the radiator somewhere. Just looking for pointers if I'm headed in the right direction or how else to pursue this.

Thanks!
 
You can use a laser sight temp gun to verify temps on the engine and radiator. If you have an 86 or newer model. You need to remove the temp compensator board so that the gauge will show more accurate readings and response on the gauge. It could just be that the board is causing the gauge to do that.
 
crscx1 said:
About a year ago I installed an IPD vx cam and did a coolant flush with a new water pump at the same time, This is when the issues began to occur.
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I agree that you need to make sure the gauge is accurate before freaking out. But the timing of your events does lend some suspicion... Don't know what cam you had in before, but I'd guess a cam choice is almost certainly an attempt to increase performance. Ergo, you are generating more heat. And yes, the other side of the coin that you've already considered could be true: the cooling system could be taking away slightly less heat than it used to.

Basically on longer stretches of highway at 65-80mph the temp gauge creeps to a little more than 3/4 of the way up. It has never touched the red and stays right about there. It will drop right back down to operating temperature after I blast the heat for a minute and will stay down for a while before creeping back up. It is also worth noting that this does not happen at all while city driving, or even very spirited driving, only for longer stretches on the highway.
Click to expand...

IF the gauge is accurate, that perfectly points to the notion that you're generating heat slightly faster than you're taking it away. The thermostat has no influence on steady state conditions, only how quickly it gets there. You could put in a 160, or even remove it entirely, and eventually it will reach an equilibrium that is determined by heat generated = heat removed.

The only way that a thermostat actually controls steady state conditions is if the cooling system can take away heat much faster than it's generated. Imagine the engine is hot, and the radiator is the size of Hoover Dam, it would suck so much heat that a 180 or 190 deg thermostat would actually close up and prevent flow, thus stabilizing the engine at the thermostat opening temp.

But if the cooling capacity is marginal for the particular BTU load of that engine, that explains why running the heater is sufficient to bring engine heat back down. Try that in Death Valley and it won't be sufficient.

Bear in mind that the changes you're seeing are very likely real, but the actual coolant change might be only a few degrees in which case that's normal. If the temp gauge compensator board is playing funny business and showing a swing of 1/4 scale at that point, it's going to look a lot more dramatic than it actually is.

An honest gauge ($$) will show what's really going on, then you know whether you need to increase your cooling capacity in some fashion.

If you discover you really do have a heat problem, which you might, the next step is to measure (probes) the temp drop of the radiator itself, between inlet and outlet. The pattern can tell you a lot about surface area and flow speed. But don't worry about this part of the puzzle yet.
 
Had a similar issue on mine when I first got it.

Pulled the radiator and found that the bottom half of the fan shroud was completely packed full of dirt and grime. Carefully blew it out with compressed air and it has been good since.
 
dl242gt said:
You can use a laser sight temp gun to verify temps on the engine and radiator.
Click to expand...

That is the quickest, cheapest test. That little device will answer a lot of questions. My radiator was hot at the top and cold at the bottom because the bottom half was filled with 40 year old trash.

Gave four grandsons those things last Christmas at about $7 each. One of the granddaughters wanted one.
 
When I did the water pump, I had noticed a lot of crust and build up from the previous owner running the wrong coolant (and just age ofc). Have a new radiator on the way and will be bypassing the compensator board as well just to cover my bases. Is there a particular temp gauge you'd recommend for more accurate readings as well? I know heat is a sure way to kill one of these motors and I drive it the 4 hours back and forth to school pretty frequently so it's something I'd very much like to remedy. Thanks for your input and advice!
 
Maybe try another coolant cap. It can't hurt.

I finally bought a nice coolant pressure tester. Hand pump it up to 17psi and get the hoses rock hard, and any leaks will manifest themselves.

I also have a nice vac'n'fill tool. I vac down the system and then open the valve and coolant gets sucked in. No bleeding required.

In your case, it may just be a false high reading. One could tap into the coolant temp sensor by back probing at the computer and monitor the voltage to get a "true" reading.
 
Step 1 is to always verify coolant temps with that IR thermometer

If the gauge reads "hot" while cruising down the highway and you check to see that you're above ~205F, that's indicative of a cooling system issue. (Note, 205F is perfectly safe and barely up to operating temp. But if your stock 240 cannot maintain a temp closer to the thermostat while driving down the highway, you have issues).

Then I'd pull the thermostat and check it out. It could be cruddy inside, or could even be "lazy". You generate quite a bit of heat at higher speeds, but also dissipate it much easier from the faster moving air over the core. I believe vernet thermostats are the go to. I was able to find mine on eBay for $14. (180F)

Also be sure to have a belly pan installed, check for slipping belts on the water pump, and certainly bypass the temp board.
 
If none of the other suggestions turn up anything conclusive, check your harmonic balancer. It may be slipping (broken rubber) which means the water pump doesn't turn as much as it should.
 
Welp, my old radiator was absolutely disgusting and you could only see through it in a couple places, even when back-lit with my work light. the temp compensation board bypass when well and both these changes seem to have completely rectified the issues. Thanks again for all the help guys
 
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