Engine Cylinder Head Temp a Little High

[huntnCJfool]

I will try to keep this brief as I have not run all tests, but I am a bit perplexed at the moment. I finally had the opportunity to go on a longer test drive after swapping AMC 258 i6 / 4.2l 's and has some higher heat, but only at the cylinder head sensor port.

I have a 195 degree stat, and have two electronic sensors. One at the stock port in the head, the other is in the furthest rear block port. Now yesterday on my drive, the sensor from the head was going into the 200's on the guage, while the one in the block never got above 197. Before I did the engine swap, the same guage in the head never climbed much above 195 unless I was doing some climbing at highway speed in summer...

The t-stat is not that old, but reused from previous engine. I plan to pull it later today and see what temp it is opening but it seems to be opening and I can watch the temp drop when it does. Whether it is inconsistent I cannot say. The water pump is the same, less than 5 years old, bearing tight, I kept it. Basically I kept my entire old cooling system that worked and never overheated, and just swapped the engine which is why I am perplexed (radiator and cap are 2 years old also, heater core is 1 year old, hoses are a couple years old). I should not be having any of these reverse water pump issues people talk about because both 258s were v-belt setups. Coolant and oil are both still very clean so I cannot imagine it is a head gasket...but if it is I don't want to miss it. Would my temp just continue to climb if it was, because mine stabilized just runs hotter. Carbon buildup seems unlikely.

What could I be missing here before I drain coolant and start pulling parts and swapping sensors? I am not really concerned by any extra work even if it does ccome to needing to do the head gasket, because this engine sounds and runs great (besides the overheating!).

I am going to do the following today and will follow up with results

Get engine up to temp, check temps at various places throughout the cooling system
See if I can see coolant flowing when t-stat opens in radiator
Pull stat and test in water with a thermometer

 

[Manic Mechanic]

before you do all that pull one of your heater hoses (by the heater core preferably the top one) u may just have a air bubble not allowing the coolant to flow properly.

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[huntnCJfool]

before you do all that pull one of your heater hoses (by the heater core preferably the top one) u may just have a air bubble not allowing the coolant to flow properly.

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The heater works and both heater hoses were hot, does this eliminate this as a possibility? I fill coolant slowly and fill with a funnel into the top heater hose and into the t-stat housing heater inlet to try to prevent this issue. I also did a lot of up and downhill yesterday that should have gotten out any remaining bubbles and have a overflow tank that was topped.

Sorry just trying to be thorough as I know this helps eliminate things.

 

[huntnCJfool]

Ok I may be shutting this mystery after some more thinkin and lookin.

I think my temp sender in the head is bottomed out on the exhaust port, interfering with the coolant reading.

I just drove around for 10 minutes at 40 degrees air temp and could not get the needle to rise nearly as much. If this was a cooling system issue air temp would not matter.

The longer time I was driving yesterday and higher air temp would have allowed the exhaust to get to a higher temp overall. The fluctuations I saw could also be explained by this as the cooling system was fighting this interference at the sender.

The reason it would bottom out is I have an aftermarket speedhut cluster, and the sender was a cutable to custom length. I probably tightened it down to bottom out on the exhaust jacket. I also trust the guages because they are both "industry leading" (expensive) and they mimic each other as the needle rises and only deviate at higher RPM/Temps.

 

[Manic Mechanic]

sounds reasonable just keep monitoring it. and possibly move the wires/leads for the sender away from the exhaust.

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[huntnCJfool]

That's an affirmative! Lol # expensive heat tape looking like aluminum foil

Here are some readings

 

[Manic Mechanic]

temps don't look bad

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[huntnCJfool]

Thanks for letting me bounce ideas off.. It also dawns on me during this analysis, the sending unit placement of the AMC 258 i6 / 4.2l is somewhat wisely placed at the hottest possible area in the head furthest from the thermostat. This would allow for faster detection of overheating to shut the motor down before damage occurred I assume.

 

[Manic Mechanic]

hows that sniper efi working im really considering it for my AMC 258 i6 / 4.2l and with the complete master kit only costing 1300 it's looking even more tempting

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[huntnCJfool]

hows that sniper efi working im really considering it for my AMC 258 i6 / 4.2l and with the complete master kit only costing 1300 it's looking even more tempting

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I like it a lot so far but have not driven a whole lot, great throttle response in town and not bogging down like a rich carb. I do think it can run leaner, but I am at altitude. I just noticed on my test drive yesterday that the A/F ratio spent some time below 12- 13 when I was on the throttle so I am going to play with that now that I think this temp issue is resolved. I'm not a great fan of the touch screen, but the interface with all guages one one screen is great, and redundancy for the temp never hurts!

 

[huntnCJfool]

Backing the sender out seems to have stopped the needle rising. That was a little different, glad it turned out to be nothing and I can enjoy the 65 degree days we are having in my jeep instead of under it!

 

[TimEdway]

Thanks, it was interesting to take a look at the measurements, they brought a car with a similar problem to the service, but I think it's more complicated there, most likely you, will need to replace the cooling systems.