Mechanics

CHALLLENGE: ENGINE OVERHEATING, RAPIDLY FLUCTUATION TEMPERATURE OF LEFT SIDE HEAD AFTER RUNNING NORMALLY FOR 15 MINUTES

1989 Jeep Other • 56,000 miles

I have been working on these specific vehicles (Jeep Grand Wagoneers) for 25 years and have run into the most interesting and difficult to pinpoint problem of my career.

I have a Jeep Grand Wagoneer (AMC 360) that has a fully rebuilt motor (from a professional race engine builder from AZ with 28 years experience) with new aftermarket Edelbrock dual plane intake manifold and has been converted to TBI fuel injection.
The vehicle starts and runs normally and smoothly until it reaches thermsostat opening temp (195). It then continues to run perfectly for approximately 5-10 minutes at exactly 195.
Then, suddenly and erratically, the temperature will rise rapidly (4-8 seconds for the guage needle to travel from 195 to 240-260), sometimes hesitate for a few seconds at 230, 240 or higher, then drop just as rapidly down to 210-220 or so. This spiking will continue, with temperature readings reaching up to the guage max for serverals seconds before quikcly dropping again.

I first suspected electrical issues/resistance increases due to heat. I ran three different new sending units, then bypassed factory wiring and ran a straight wire from teh sender to the back of the cluster. I also swapped in three different clusters (one used and known to work correctly). I also grounded the cluster directly.

Lastly, and most interestingly, I ran a code scanner simultaneously to monitor the TBI fuel injection temp sender and it stays right around the thermostat temp at ALL TIMES (188-200). This FI temp sender is in the same section of large, front cooling jacket, but on the other end of the intake manifold opposite the factory sender, on the other side of the thermostat housing.

I bled the system of air several times/burped it. Tested cooling system pressure (held perfect pressure for 25 minutes without a leak). Checked oil and coolant for signs of head gasket leak (oil in water, water in oil) and both were negative. I have also installed 3 different brand new thermostats, two brands, and had the same symptoms all three times.

Again, the car runs correctly, with temperature steadily, slowly rising until it reaches thermostat opening temps, and then continues to run correctly for 5-10 minutes at a rock solid, stable temp of 195-200, until the temperature readings suddenly start spiking and falling.

Since I was getting the radically different temp sender readings on opposite ends of the intake manifold coolant water jacket, I started using an infrared thermometer to test the block and heads on both sides, from underneath the car, to observe temperatures. This testing revealed that, indeed, the driver's side/left side block and head WAS suffering sudden and radical changes in temperature. With block surface temps on the left suddenly rising 40-50 degrees (240-250 degrees) over the course of 10-15 seconds, staying there, and then dropping again to approx 200 degrees. This cycle continues as long as I dare run the vehicle. Right side/passenger block and head stays pretty much stable at around 200.

If any of you experienced, old-time wrenchers with excellent diagnostic skills has any ideas on how to proceed, I would be forever grateful.

Thank you,
Bobby in LA
Avatar
Norbertb
September 12, 2011.



First thing, if you are getting the correct temp at the front for the computer sender then I wold suspect positioning of the gauge sensor. Itf this thing flows water like a small block chevy, then what happens is the water goes through the block and enters the head at the rear, hence higher temps there than in front. But as this is a n AMC motor I can't say for sure. I would suspect that it could be a partial blockage in the head or an incorrect head gasket. You said you tested the cooling system for leaks and it held perfect pressure, but did you not test the radiator cap? RAdiator caps are a weak spot on these systems. Also is this a closed rad system or a regular one and has the worng rad cap on it? One other thing, doe the old manifoldhave a water crossover at teh rear and the edelbrock doesn't? One last possible scenario, on the LS1 engine they had to run a small pipe from head to head to elimnate air that was trapped in the head an dthis may possibly wha tis happening, you are seeing the temp drop when the air ifs forced out.

Hmac300
Sep 12, 2011.
Thanks for the input hmac. The radiator cap has been tested (it's a 16psi system) and the cap has been replaced three times just to be sure.
I first suspected an air bubble and it has now been bled three times, by burping, removing the temp senders and bleeding, bleeding at the heater core and elevating/angling the vehicle while bleeding. Since I've had this jeep in the shop and have been trying to deal with this for a month, and have been running it, with the same results for so long (at least 2 dozen start and run cycles with the same results), I doubt that any air could still be trapped even if the air had not been removed through bleeding. Not sure about the water crossover in the manifold since I would have to remove it to check. Also don't have the factory piece any more. But have installed the same dual plane performer Edelbrock manifolds on about a dozen Grand Wagoneers with AMC 360s in the past 5 years without incident. Of course casting error or slag could be a possibility.

But, if there is a coolant obstruction in the manifold or head, why would the temperature remain perfectly stable for 5-10 minutes after the thermostat opens and then suddenly start the spiking temperature cycle?

This is the reason why I also ruled out radiator or water pump issues. Because it warms up slowly and normally and stays at thermostat temp for quite a while before the temperature spiking begins (usually for 20 minutes from a cold start).

Tiny
Norbertb
Sep 13, 2011.
Because it may be a piece floating around inside the head and whenit gets in the way the temp goes up until it moves then the temp goes down. The only other thing I can think of is maybe the impeller blade onteh pump is loose or slipping then grabs then slips.

Hmac300
Sep 13, 2011.
If it was the water pump or an intermittant impeller failure wouldn't it also affect the passenger side head and block? Ditto with the radiator.
If there was an obstructive piece floating around in the coolant channels, is it likely that it would block a passage only after the same 20 minutes or so of orderly warmup and then 10 minutes of normal, stable temp running at the thermostat opening temperature? And then always in the same head/block section with the same timing?
The repeatability (I've gone through well over a dozen identical running cylces), the 10 minutes of steady running at 195 prior to the heat spiking starting, originally led me to rule out water pump, radiator or moving obstruction. I always believed that head/block expansion and heat factored into the equation somehow.

Tiny
Norbertb
Sep 13, 2011.
Teh answers i've given are what it Could be, if you have worked on these things you know the only real way to tell anything is to pull the head off an dsearch around for a casting problem, looseparticles, head gasket, etc. I know you are trying to find ananswer without pulling the head off and going through the work. Maybe if you pull the sender off and check for debris or if you can get one of the cheap cameras like at hrabor freight you might be able to snake that down into the jacket and see if you see anything by just pulling sender. If not you'll have to take it apart.

Hmac300
Sep 13, 2011.
One other thing as i've been pondering this over in my brain. I dont' think you had this problem until you moved the sender for the gauge. So if everything is going ok then maybe moving the gauge to the front of the manifold is where it will eliiminate the problem. This amy abe and inherent thing with the amc engine and normally does this. Every engine has it own particualar quirks that the manufacturers don't really say alot about. The only true way to see if this is true is to get another engine with the sender mounted in the same place and actually see if it does it there. I kind of think that this may be the case and you are actually beating yourself up for nothing.

Hmac300
Sep 14, 2011.
Hi Hmac,
The sending unit for the factory gauge is in the same location that it was originally in when this issue occurs. However, when I move the factory sending unit next to the new fuel injection sending unit, on the other side of the manifold, the temperature stays stable (just like the reading on the code reader coming from the FI sender). I have installed several different sending units in the factory sender spot and always get the same results (the radical temperature spiking).
The problem can't be an inherent engine problem since the temp sender giving the erratic signals is in the factory location and I have never experienced this on, literally, 40-50 of these motors that I have worked on.
I didn't want to influence the diagnostic analysis but the ony thing that I have been able to come up with that makes a bit of sense is that there is a slight head gasket leak in the left front cylinder pair that only begins to leak once the engine has been running for 20 minutes or so and the head and block expand to a certain degree due to the normal heat cycle of the iron (both block and head iron). This intermitant head gasket leak then sends occassional bursts of extremely high temperature combustion gases into the coolant ports on that side only, suddenly and violently spiking the temperature of that section of the engine and head (since the other side remains stable temperatures). I just don't understand why the leak of combustion gas would then suddenly stop once a certain temperature is reached (maybe, when the block and head reach 250 degrees and over, the metal expands to such a point that the gasket is again compressed and stops leaking. Then when the temperature drops, the leak starts up again and this happens over and over).
I am just astounded that such a sudden increase in left side block and head would not also spike the temperature of the entire coolant so that the right side mounted temperature gauge (for FI) is affected and shows the same spikes.
It may be that the coolant travels from the right to the left side of the motor and then is dumped back into the radiator, which is a huge, very efficient unit with powerful fan that drops inlet temperature very significantly by the time the coolant exits the outlet port. So, the cooled coolant enters the right, stable temp side, but is superheated momentarily on the left side where the combustion leak is before it goes back into the radiator and is rapidly cooled causing it to drop to the steady, stable temperature I have observed.
I wish I had an AMC block water jacket/coolant circulation diagram to see if this even makes sense but cannot find one anywhere. If you have any ideas where to look, that would be very helpful.
The other spoiler of this theory is that a local friend with a combusiton gas tester supposedly tested the radiator for me and found no sign of combustion gases.
Any ideas?

Tiny
Norbertb
Sep 14, 2011.
I used to work in engineering for an auto manufcturer as well as a mechanic, it probably does get to the right head first then the left. If it is leaking in thehaead gasket as you say or think then I would think a dose of block sealer would help that matter. But it still leads me to beleive that there is a head gasket problem or small crack. If this has aluminum heads then it could be it has a hard pin for a locating dowel for the heads. These type of dowels make the head go all over until it gets heated upand sometimes crack the head. That is why most manufacturers use the spring type locating dowel. But if memory serves me correct the AMC has iron heads so that theory is out the window. One other thing is coolant. If the red dexcool was added to the vehicle and then green was put in these type of antifreezes tend to gel inside the cylinder block, especially if they are leftlow on coolant for a time or while running. Other which cold would explain the overheating problem then cooling then overheating. The only other thing I can advise is to get a radiator cleaner like Prestone radiator clean which is oxyalic acid and empty all the coolant out, including the block, just add water and the coolant cleaner, then drop the lower rad hose so it will all flow out including aluminum pieces from the silicone in the coolante eating away atthe aluminum parts in the motor. Other than that I really have no idea whatelse to do without tearing it apart and physically looking in the block and head coolant passages. The only other possible thing that I can think of is that athe head gasket could have been installed upside down which would put the rear coolant passages in the front and fronts in the rear. I'd have to bet they are different size holes. The whole trouble with this is that you have got what someone els has done and now you are stuck with it to try to fix it. I have no other ideas on what to do with this other than taking it apart. I'm sure you would find something then.

Hmac300
Sep 14, 2011.
Thank you for the feedback.
Yes, the heads are the factory iron heads (just fully machined and rebuilt).
The engine builder has a great reputation and builds AMC race motors regularly so I'd be surprised if they installed a head gasket upside down, but I realize those things happen (I've been guilty of similar mistakes).
The coolant has all been new, green standard Prestone in a 50/50 mix. I've also drained all coolant and run it on straight water with the same results.
If I give a block sealer a try, do you have one you trust and recommend. In the last 20 years I have never used one and was always affraid that it would cause problems with coolant passage and radiator obstruction. What has your experience been?
Do you drain the sealer out again after a short time and replace only pure coolant/water?
Thanks a bunch,
Norbert

Tiny
Norbertb
Sep 14, 2011.
I was always prtial to the metal type but I thinkmost of them are ok. The passages are pretty large and if the rad clogs then it wasn't in good shape anyhow. Once it got up to operatingtemp and run for a little while then drain it if you like, that's up to you. And use the old 50/50 mix for best results. I was wondering, if you have any cold spotsontherad when it's warmed up. If you had any cold spots then it's not in good shape as it should feel the same temp all over. But you probably alredy know that. Anyhow good luck if yo do happen to find the problem let me know. But it hink it's going to have to be torn down to find anything.

Hmac300
Sep 14, 2011.
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